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Michael Olsen edited this page Dec 25, 2024 · 207 revisions

This guide introduces the general concepts involved when developing an application using CefSharp. It's important to remember that CefSharp is a .Net wrapper around the Chromium Embedded Framework (CEF). CEF is an open source project based on the Google Chromium project. Unlike the Chromium project itself, which focuses mainly on Google Chrome application development, CEF focuses on facilitating embedded browser use cases in third-party applications.

CEF is based on the multi-process Chromium Content API and as a result only a subset of the features that exist in Chromium are currently available. For example, support for extensions is limited, only a subset of the Extension API is implemented.

The CEF project has its own website and Support Forum if you're dealing with a low level problem or your question is pretty generic you can search or post on the forum. Be sure to mention which CEF version you're using. CefSharp versions look like 73.1.130, which maps to CEF 73.1.13+g6e3c989+chromium-73.0.3683.75. Open chrome://version/ or check your packages.config to easily determine the version. Post on CEF Support Forum before opening an issue on the CEF Issue Tracker.

It's important to remember that CefSharp is limited by the API that CEF exposes, and even then not all of the CEF API is currently implemented. If you are chasing a particular feature then check through the CEF C++ headers or CEF API Doc. If there is a piece of the CEF API that is not currently exposed, then you can implement it yourself and submit a PR for inclusion in the main project.

This document is based on CEF General Usage Wiki

CefSharp provides four different implementations, WinForms, WPF, WPF.HwndHost and OffScreen. The WPF and OffScreen versions use the OffScreen Rendering(OSR) rendering mode. In OSR mode each frame is rendered to a buffer and then either drawn on the screen as in the case of WPF or available as a Bitmap in OffScreen. Performance of the WPF version is slower than the WinForms version. Wpf.HwndHost implementation is equivilent ot hosting the WinForms version in WPF with support for WPF Data Binding.

All versions use the CefSharp, CefSharp.Core and CefSharp.Core.Runtime libraries, as a result much of the API is used exactly the same within all three flavors. This limits code duplication and reduces the maintenance burden of adding a new feature.

Table of Contents

Release Notes

Release notes are available for each version at https://github.com/cefsharp/CefSharp/releases please take the time to read over them if you're having problems or curious about what's changed. Check the Known Issues section if you're having problems and there are usually notes that contain useful info about a release.

Software Requirements

CefSharp uses Visual C++(VC++) to interface with the underlying native C++ API, as a result it will only run on Windows. (There is no Windows APP Store version). Each CefSharp release has it's own branch, see https://github.com/cefsharp/CefSharp#release-branches for details and requirements for each branch are listed there.

CefSharp requires:

Notes:

AnyCPU Support

Newer versions now support targeting AnyCPU, see https://github.com/cefsharp/CefSharp/issues/1714 for details on how to implement this. The same technique can be used to move libcef.dll, etc to a different folder or common location on disk.

Need to Know/Limitations

  • Specifying a CachePath is required for persistence of cookies, saving of passwords, etc, an In-Memory cache is used by default (similar to Incognito). See Initialize and Shutdown section below for an example of Initializing CEF with a CachePath below.
  • You can clear the disk cache using see Network.clearBrowserCache see #3158 for details on executing DevTools commands.
  • Add an app.manifest to your app for HiDPI support, app compatibility (running on Windows 10) and tooltips in WinForms. The examples contain sample app.manifest files. This is very important (http://magpcss.org/ceforum/viewtopic.php?f=6&t=14721)
  • An error in the logs similar to Check failed: fallback_available == base::win::GetVersion() > base::win::VERSION_WIN8 (1 vs. 0) is a sign your application needs a app.manifest with the relevant compatibility entries.
  • CEF can only be Initialized/Shutdown once per process, see the section below for full details, this is a limitation of the underlying Chromium framework.
  • Only runs in the default AppDomain, there are some workarounds like those at https://github.com/flole/CefSharp.AppDomain and https://github.com/stever/AppHostCefSharp
  • Due to limited resources only a single version is supported at a time, see https://github.com/cefsharp/CefSharp#release-branches to see which version is current. If you're using an older version and encounter a problem you'll have to upgrade to the current supported version.
  • Only runs on Windows and no App Store version.
  • .Net Core is supported though additional steps are required see https://github.com/cefsharp/CefSharp.MinimalExample#net-core-support
  • Sandboxing has not been implemented as it's technically infeasible to add support directly into CefSharp, see #697 for details.
  • WinForms on screen keyboard potentially can benefit from disable-usb-keyboard-detect command line argument https://github.com/cefsharp/CefSharp/issues/1691#issuecomment-323603277
  • WPF users with High DPI monitors are recommended to install .Net 4.6 on their target machines, as there is a bug in the .Net Framework that can potentially cause a MILERR_WIN32ERROR Exception see #2035 for details
  • Google Earth currently requires SharedBufferArray which is disabled by default see https://github.com/cefsharp/CefSharp/discussions/3826#discussioncomment-1383028 on how to enable.

Examples

The CefSharp source code contains examples of many different features. There is also the MinimalExample project which uses the latest Nuget packages to provide very simple Browser implementations. The MinimalExample is the best place to get started, download this project and get it running for a base reference to make sure everything works on your system.

https://github.com/cefsharp/CefSharp.MinimalExample

Logging

By default CEF maintains its own log file ('Debug.log') in your application's executing folder e.g. bin. To disable logging change settings.LogSeverity, and to change the file name/path use settings.LogFile.

When debugging a problem, the first place to check is this log file as it contains low level Chromium messages. If you see errors or warnings then search on http://magpcss.org/ceforum/index.php and https://bitbucket.org/chromiumembedded/cef/issues?status=new&status=open

Processes

CEF uses the same multiprocess model as Chromium. The main process which handles window creation and painting is referred to as the browser process. This is generally the same process as the host application and the majority of the application logic will run in the browser process. Blink rendering and JavaScript execution occur in a separate render process. Some application logic, such as JavaScript bindings, will also run in the render process.

  • Render Processes (--type=renderer) - V8(Javascript) and rendering
  • GPU Process (--type=gpu-process) - handles GPU accelerated compositing
  • Network Service (--type=utility --utility-sub-type=network.mojom.NetworkService) - Entire Chromium network stack runs in this process
  • Storage Service (--type=utility --utility-sub-type=storage.mojom.StorageService) - html5 storage e.g. localStorage
  • Audio Service (--type=utility --utility-sub-type=audio.mojom.AudioService) - Playing of audio
  • CrashPad Handler (--type=crashpad-handler) - creates crash dumps

By default a spare renderer process may be created on initial browser creation or cross- origin navigation. This spare process may be used with a future cross-origin navigation or discarded on when Cef.Shutdown has been called.

CefSharp comes with a process called CefSharp.BrowserSubProcess.exe which will be spawned multiple times to represent separate processes as described above. Opening Task Manager and seeing multiple instances of CefSharp.BrowserSubProcess.exe is perfectly normal and required for the browser to function correctly. It is possible as of version 51.0.0 to provide your own custom BrowserSubProcess. An example of self hosting the BrowserSubProcess using your own executable using WinForms is available as part of the MinimalExample

Resources:

Threads

CEF uses multiple threads for different levels of processing. The browser process for example contains the following commonly-referenced threads:

  • UI thread is the main thread in the browser process. By default CefSharp uses setting.MultiThreadedMessageLoop = true so the CEF UI thread is different to your main application thread
  • IO thread is used in the browser process to process IPC and network messages
  • FILE thread is used in the browser process to interact with the file system
  • RENDERER thread is the main thread in the renderer process

Initialize and Shutdown

Can only called Initialize once per process (application). Running multiple instances of your app is possible, you'll need to provide unique CachePath for each instance, see CefSettings section below.

See Request Context (Browser Isolation) for details on how to change settings at runtime, isolate browser instances, set different cache paths for different instances.

It's important to note that it's necessary to initialize the underlying CEF library. This can be achieved in one of two ways, manually calling Cef.Initialize before creating your first ChromiumWebBrowser instance, secondly if you don't need to specify any custom settings then the first ChromiumWebBrowser instance you create will call Cef.Initialize if it hasn't been called already. For those wishing to specify some custom settings then you can initialize CEF yourself like below:

public static void Init()
{
    var settings = new CefSettings();

    // Increase the log severity so CEF outputs detailed information, useful for debugging
    settings.LogSeverity = LogSeverity.Verbose;
    // By default CEF uses an in memory cache, to save cached data e.g. to persist cookies you need to specify a cache path
    // NOTE: The executing user must have sufficient privileges to write to this folder.
    settings.CachePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache");

    Cef.Initialize(settings);
}

For Cef.Shutdown the WinForms and WPF instances of ChromiumWebBrowser the relevant Application Exit event is hooked and Cef.Shutdown() called by default. Set CefSharpSettings.ShutdownOnExit = false; to disable this behavior. This value needs to be set before the first instance of ChromiumWebBrowser is created as the event handlers are hooked in the static constructor for the ChromiumWebBrowser class.

It's important to note CEF that Initialize/Shutdown MUST be called on your main application thread (typically the UI thread). If you call them on different threads, your application will hang.

An example of calling Initialize/Shutdown manually using WinForms, the same can be applied to WPF and console applications that use the CefSharp.OffScreen package (The OffScreen example at https://github.com/cefsharp/CefSharp.MinimalExample is an excellent place to start, there is also one in the main project repository that's a little more advanced).

public class Program
{
        [STAThread]
        public static void Main()
        {
            //We're going to manually call Cef.Shutdown below, this maybe required in some complex scenarios
            CefSharpSettings.ShutdownOnExit = false;

            //Perform dependency check to make sure all relevant resources are in our output directory.
            Cef.Initialize(new CefSettings(), performDependencyCheck: true, browserProcessHandler: null);

            var browser = new BrowserForm();
            Application.Run(browser);
	    
            //Shutdown before your application exists or it will hang.
            Cef.Shutdown();
        }
}

In summary

  • Cef.Initialize and Cef.Shutdown can only called Initialize once per process(application). There is no way around this, so only call Shutdown when you're finished using CefSharp.
  • Cef.Initialize and Cef.Shutdown must be called on the same thread.
  • Cef.Initialize will be called for you implicitly if you create a new ChromiumWebBrowser instance and haven't already called Cef.Initialize.
  • For the WinForms and WPF instances of ChromiumWebBrowser the relevant Application Exit event is hooked and Cef.Shutdown() called by default. Set CefSharpSettings.ShutdownOnExit = false; to disable this behavior. This value needs to be set before the first instance of ChromiumWebBrowser is created as the event handlers are hooked in the static constructor for the ChromiumWebBrowser class.
  • In CefSharp.OffScreen you must explicitly call Cef.Shutdown() before your application exists or it will hang.

CefSettings and BrowserSettings

The CefSettings structure allows configuration of application-wide CEF settings. Some commonly configured members include:

  • AcceptLanguageList comma delimited ordered list of language codes without any whitespace that will be used in the "Accept-Language" HTTP header.
  • BrowserSubprocessPath The path to a separate executable that will be launched for sub-processes. Typically there is no need to change this.
  • MultiThreadedMessageLoop the default is True in CefSharp, though it is possible to integrate CEF into your apps existing message loop see MultiThreadedMessageLoop Section below.
  • CommandLineArgsDisabled Set to true to disable configuration of browser process features using standard CEF and Chromium command-line arguments.
  • RootCachePath The root directory that all CefSettings.CachePath and RequestContextSettings.CachePath values must have in common. If this value is empty and CefSettings.CachePath is non-empty then it will default to the CefSettings.CachePath value. If this value is non-empty then it must be an absolute path. A non-empty RootCachePath can be used in conjunction with an empty CefSettings.CachePath in instances where you would like browsers attached to the Global RequestContext (the default) created in "incognito mode" and instances created with a custom RequestContext using a disk based cache. See the RequestContext section below for more details.
  • CachePath The location where data for the global browser cache will be stored on disk. In this value is non-empty then it must be an absolute path that is must be either equal to or a child directory of CefSettings.RootCachePath (if RootCachePath is empty it will default to this value). If the value is empty then browsers will be created in "incognito mode" where in-memory caches are used for storage and no data is persisted to disk. HTML5 databases such as localStorage will only persist across sessions if a cache path is specified. Can be overridden for individual RequestContext instances via the RequestContextSettings.CachePath value. See the RequestContext section below for more details.
  • Locale The locale string that will be passed to Blink. If empty the default locale of "en-US" will be used. Also configurable using the "lang" command-line switch. Change this to set the Context menu language as well.
  • LogFile The directory and file name to use for the debug log. If empty, the default name of "debug.log" will be used and the file will be written to the application directory. Also configurable using the "log-file" command-line switch.
  • LogSeverity The log severity. Only messages of this severity level or higher will be logged. Also configurable using the "log-severity" command-line switch with a value of "verbose", "info", "warning", "error", "error-report" or "disable".
  • ResourcesDirPath The fully qualified path for the resources directory. If this value is empty the cef.pak and/or devtools_resources.pak files must be located in the module directory. Also configurable using the "resources-dir-path" command-line switch.
  • LocalesDirPath The fully qualified path for the locales directory. If this value is empty the locales directory must be located in the module directory. This value is ignored on Mac OS X where pack files are always loaded from the app bundle Resources directory. Also configurable using the "locales-dir-path" command-line switch.
  • RemoteDebuggingPort Set to a value between 1024 and 65535 to enable remote debugging on the specified port. For example, if 8080 is specified the remote debugging URL will be http://localhost:8080. CEF can be remotely debugged from any CEF or Chrome browser window. Also configurable using the "remote-debugging-port" command-line switch.

There are many settings and command line arguments that can influence the way CEF behaves. Here are some examples:

public static void Init()
{
    // Specify Global Settings and Command Line Arguments
    var settings = new CefSettings();

    // By default CEF uses an in memory cache, to save cached data e.g. to persist cookies you need to specify a cache path
    // NOTE: The executing user must have sufficient privileges to write to this folder.
    settings.CachePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache");;

    // There are many command line arguments that can either be turned on or off

    // Enable WebRTC                            
    settings.CefCommandLineArgs.Add("enable-media-stream");
    
    //Disable GPU Acceleration
    settings.CefCommandLineArgs.Add("disable-gpu");

    // Don't use a proxy server, always make direct connections. Overrides any other proxy server flags that are passed.
    // Slightly improves Cef initialize time as it won't attempt to resolve a proxy
    settings.CefCommandLineArgs.Add("no-proxy-server"); 

    Cef.Initialize(settings);
}

There are some settings which can be applied to a specific ChromiumWebBrowser instance. If you're using WPF, you can specify BrowserSettings in XAML.

var browser = new ChromiumWebBrowser(url)
{
    BrowserSettings =
    {
        DefaultEncoding = "UTF-8",
        WebGl = CefState.Disabled
    }
};
<!--xmlns:cefSharpCore="clr-namespace:CefSharp;assembly=CefSharp.Core"-->
<!--xmlns:cefSharpWpf="clr-namespace:CefSharp.Wpf;assembly=CefSharp.Wpf"-->

<cefSharpWpf:ChromiumWebBrowser>
    <cefSharpWpf:ChromiumWebBrowser.BrowserSettings>
        <cefSharpCore:BrowserSettings DefaultEncoding="UTF-8"/>
    </cefSharpWpf:ChromiumWebBrowser.BrowserSettings>
</cefSharpWpf:ChromiumWebBrowser>

IBrowser, IFrame and IBrowserHost

The IBrowser and IFrame objects are used for sending commands to the browser and for retrieving state information in callback methods. Each IBrowser object will have a single main IFrame object representing the top-level frame and zero or more IFrame objects representing sub-frames.

For example, a browser that loads two HTML <iframe>s will have three IFrame objects (the top-level frame and the two <iframe>s).

To load a URL in the browser main frame:

browser.MainFrame.LoadUrl(someurl);

CefSharp provides many extension methods to make executing common tasks easier. See WebBrowserExtensions for the source of these methods and to get a better understanding of how common tasks are performed.

IBrowserHost represents the more low level browser methods.

Handlers

CefSharp provides some events for convenience like the following (See IWebBrowser API doc for all common events and detailed information on their usage):

These are simple events that expose a small percentage of the underlying handlers that CEF provides. These events are only called for the main browser, for popup handling you can access the notifications using IDisplayHandler and ILoadHandler.

To determine when a page has finished loading I recommend using LoadingStateChanged over FrameLoadEnd. It's important to remember that finished loading is different to finished rendering. There is currently no method of determining when a web page has finished rendering (and unlikely ever will be as with features like flash, dynamic content, animations, even simple tasks like moving your mouse or scrolling will cause new frames to be rendered).

IDialogHandler, IDisplayHandler, IDownloadHandler, IContextMenuHandler, ILifeSpanHandler, ILoadHandler and IRequestHandler are some of the more common handlers (see the source/API doc for the rest). These simply wrap the underlying CEF handlers in a convenient .NET fashion. For example CEF's CefDownloadHandler is IDownloadHandler in CefSharp. Implementing these handlers will provide you access to the underlying events and callbacks that are the foundation of CEF. A number of handlers' members can be executed in an async fashion using a callback. All the handlers follow a consistent pattern: those that return a bool are asking you whether you'd like to handle this yourself. If no, then return false for the default action. Return true if you will handle it yourself.

They are basic interfaces which you implement and then assign to your ChromiumWebBrowser instance. e.g.

browser.DownloadHandler = new DownloadHandler();

Ideally you should set handlers immediately after your ChromiumWebBrowser instances have been instantiated. See the Example projects in the source for more detailed examples, there are currently no default implementations available so you have to implement every method. (If you wish to contribute default implementations then submit a pull request).

Some general notes about the handlers

It is possible to modify the response using a ResponseFilter. See section below.

Resource Handling

CEF supports two approaches for loading resource requests from memory/disk/database

  1. The Scheme Handler approach allows registration of a handler for requests targeting a particular origin (scheme + domain).
  2. The Request Interception approach allows handling of arbitrary requests at the application's discretion.

Use the HTTP(S) scheme instead of a custom scheme to avoid a range of potential issues.

If you choose to use a custom scheme (anything other than http://, https://, etc) you must register it with CEF so that it will behave as expected. If you would like your custom scheme to behave similar to HTTP (support POST requests and enforce HTTP access control (CORS) restrictions) then it should be registered as a "standard" scheme. If you are planning to perform cross-origin requests to other schemes or send POST requests via XMLHttpRequest to your scheme handler then you should use the HTTP scheme instead of a custom scheme to avoid potential issues. IsSecure and IsCorsEnabled params were added recently.

Handlers can be used with both built-in schemes (http://, https://, etc) and custom schemes. When using a built-in scheme choose a domain name unique to your application (like myapp or internal). Implement the ISchemeHandlerFactory and IResourceHandler classes to handle the request and provide response data. See ResourceHandler for the default implementation of IResourceHandler, which has lots of useful static helper methods.

Scheme Handler

Handlers can be used with both built-in schemes (HTTP, HTTPS, etc) and custom schemes. When using a built-in scheme choose a domain name unique to your application (like myapp or internal). Implement the ISchemeHandlerFactory and IResourceHandler classes to handle the request and provide response data. See ResourceHandler for the default implementation of IResourceHandler, which has lots of useful static helper methods.

A scheme handler is registered via the CefSettings.RegisterScheme function. For example, you can register a handler for 'https://cefsharp.test/' requests (there is another example below and there are working examples in the project source):

settings.RegisterScheme(new CefCustomScheme
{
	SchemeName = "https",
	DomainName = "cefsharp.test",
	SchemeHandlerFactory = new FolderSchemeHandlerFactory(rootFolder: @"..\..\..\..\CefSharp.Example\Resources",
							hostName: "cefsharp.test", //Optional param no hostname/domain checking if null
							defaultPage: "home.html") //Optional param will default to index.html
});

The FolderSchemeHandlerFactory is a simple default implementation for reading files from disk using a scheme handler. You can use either a custom scheme (In other words, you can provide a URL in the form customscheme://folder/yourfile) or a standard scheme (https://, https://).

An example of implementing your own factory might look like:

public class CefSharpSchemeHandlerFactory : ISchemeHandlerFactory
{
	public const string SchemeName = "custom";

	private static readonly IDictionary<string, string> ResourceDictionary;

	static CefSharpSchemeHandlerFactory()
	{
		ResourceDictionary = new Dictionary<string, string>
		{
			{ "/home.html", Resources.home_html },
			{ "/bootstrap/bootstrap.min.css", Resources.bootstrap_min_css },
			{ "/bootstrap/bootstrap.min.js", Resources.bootstrap_min_js },
			{ "/BindingTest.html", Resources.BindingTest },
			{ "/ExceptionTest.html", Resources.ExceptionTest },
			{ "/PopupTest.html", Resources.PopupTest },
			{ "/SchemeTest.html", Resources.SchemeTest }
		};
	}

	public IResourceHandler Create(IBrowser browser, IFrame frame, string schemeName, IRequest request)
	{
		//Notes:
		// - The 'host' portion is entirely ignored by this scheme handler.
		// - If you register a ISchemeHandlerFactory for http/https schemes you should also specify a domain name
		// - Avoid doing lots of processing in this method as it will affect performance.
		// - Uses the Default ResourceHandler implementation

		var uri = new Uri(request.Url);
		var fileName = uri.AbsolutePath;

		string resource;
		if (ResourceDictionary.TryGetValue(fileName, out resource) && !string.IsNullOrEmpty(resource))
		{
			var fileExtension = Path.GetExtension(fileName);
			return ResourceHandler.FromString(resource, , mimeType: Cef.GetMimeType(fileExtension));
		}

		return null;
	}
}

The ResourceHandler is provided as a default implementation of IResourceHandler and contains many static helper methods for creating classes. See the Resource Handler section below for further details.

A few examples of using the static methods are:

ResourceHandler.FromStream(stream, mimeType);
ResourceHandler.FromString(htmlString, includePreamble:true, mimeType:Cef.GetMimeType(fileExtension));
ResourceHandler.FromFilePath("CefSharp.Core.xml", mimeType);

Finally, you have to register this scheme handler using some code like this:

public static void Init()
{
	// Pseudo code; you probably need more in your CefSettings also.
	var settings = new CefSettings();

	settings.RegisterScheme(new CefCustomScheme
	{
		SchemeName = "custom",
		SchemeHandlerFactory = new CefSharpSchemeHandlerFactory()
	});

	Cef.Initialize(settings);
}

It's important that the scheme registration takes place before Cef.Initialize() is called.

Request Interception

IResourceRequestHandler.GetResourceRequestHandler supports the interception of arbitrary requests. It uses the same IResourceHandler class as the scheme handler approach. The ResourceHandler is provided as a default implementation of IResourceHandler and contains many static helper methods for creating classes. See the Resource Handler section below for further details.

public class CustomResourceRequestHandler : CefSharp.Handler.ResourceRequestHandler
{
	protected override IResourceHandler GetResourceHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request)
	{
		//ResourceHandler has many static methods for dealing with Streams, 
		// byte[], files on disk, strings
		// Alternatively ou can inheir from IResourceHandler and implement
		// a custom behaviour that suites your requirements.
		return ResourceHandler.FromString("Welcome to CefSharp!", mimeType: Cef.GetMimeType("html"));
	}
}

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		//Only intercept specific Url's
		if (request.Url == "http://cefsharp.test/" || request.Url == "https://cefsharp.test/")
		{
			return new CustomResourceRequestHandler();
		}

		//Default behaviour, url will be loaded normally.
		return null;
	}
}

browser.RequestHandler = new CustomRequestHandler();

The IWebBrowser.RegisterResourceHandler and IWebBrowser.UnRegisterResourceHandler extension methods provide a simple means of providing an IResourceHandler for a given Url.

You could for example request a fictitious URL and provide a response just as if the site was real.

ResourceHandler

Both ISchemeHandlerFactory and IResourceRequestHandler.GetResourceHandler use the IResourceHandler interface to represent the response (stream + headers + status codes, etc). There is a default implementation of IResourceHandler which is simply ResourceHandler.

ResourceHandler contains many static methods for convenience

A few examples of using the static methods are:

ResourceHandler.FromStream(stream, mimeType);
ResourceHandler.FromString(htmlString, includePreamble:true, mimeType:Cef.GetMimeType(fileExtension));
ResourceHandler.FromFilePath("CefSharp.Core.xml", mimeType);

The source contains detailed examples of ISchemeHandlerFactory.

Examples of how to implement ResourceHandler.ProcessRequestAsync. If you require complete control then implement IResourceHandler, however in most cases this is not necessary.

//A simple example of a ResourceHandler that downloads a file from the internet.
//A task is called to perform processing then executes the callback when the response is ready.
//You could do Database queries + html generation or other backend type operation
public class ExampleResourceHandler : ResourceHandler
{
	public override CefReturnValue ProcessRequestAsync(IRequest request, ICallback callback)
	{
		Task.Run(() =>
		{
			using (callback)
			{
				var httpWebRequest = (HttpWebRequest)WebRequest.Create("https://raw.githubusercontent.com/cefsharp/CefSharp/master/README.md");

				var httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();

				// Get the stream associated with the response.
				var receiveStream = httpWebResponse.GetResponseStream();
				var mime = httpWebResponse.ContentType;

				var stream = new MemoryStream();
				receiveStream.CopyTo(stream);
				httpWebResponse.Close();

				//Reset the stream position to 0 so the stream can be copied into the underlying unmanaged buffer
				stream.Position = 0;

				//Populate the response values
				ResponseLength = stream.Length;
				MimeType = mime;
				StatusCode = (int)HttpStatusCode.OK;
				Stream = stream;

				callback.Continue();
			}
		});

		return CefReturnValue.ContinueAsync;
	}
}

Response Filtering

IResourceRequestHandler.GetResourceResponseFilter() supports filtering of data received in response to requests. You can retrieve the raw response data, you can append data to a response, like injecting some custom CSS at the end of a file. You can rewrite a response if required. Can be used to receive the response of any request, AJAX(XHRHttpRequest)/POST/GET.

The basic example of getting the response as a UTF8 string is:

public class CustomResourceRequestHandler : CefSharp.Handler.ResourceRequestHandler
{
	private readonly System.IO.MemoryStream memoryStream = new System.IO.MemoryStream();

	protected override IResponseFilter GetResourceResponseFilter(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IResponse response)
	{
		return new CefSharp.ResponseFilter.StreamResponseFilter(memoryStream);
	}

	protected override void OnResourceLoadComplete(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IResponse response, UrlRequestStatus status, long receivedContentLength)
	{
		//You can now get the data from the stream
		var bytes = memoryStream.ToArray();

		if (response.Charset == "utf-8")
		{
			var str = System.Text.Encoding.UTF8.GetString(bytes);
		}
		else
		{
			//Deal with different encoding here
		}
	}
}

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		//Only intercept specific Url's
		if (request.Url == "http://cefsharp.github.io/" || request.Url == "https://cefsharp.github.io/")
		{
			return new CustomResourceRequestHandler();
		}

		//Default behaviour, url will be loaded normally.
		return null;
	}
}

browser.RequestHandler = new CustomRequestHandler();

Currently StreamResponseFilter is the only filter provided as part of the framework.

A simple response filter that copies dataIn to dataOut. Data is streamed in chunks, typically 64kb in size.

/// <summary>
/// PassThruResponseFilter - copies all data from DataIn to DataOut.
/// Upstream documentation link
/// https://magpcss.org/ceforum/apidocs3/projects/(default)/CefResponseFilter.html#Filter(void*,size_t,size_t&,void*,size_t,size_t&)
/// </summary>
public class PassThruResponseFilter : IResponseFilter
{
	bool IResponseFilter.InitFilter()
	{
		return true;
	}

	FilterStatus IResponseFilter.Filter(Stream dataIn, out long dataInRead, Stream dataOut, out long dataOutWritten)
	{
		if (dataIn == null)
		{
			dataInRead = 0;
			dataOutWritten = 0;

			return FilterStatus.Done;
		}

		//Calculate how much data we can read, in some instances dataIn.Length is
		//greater than dataOut.Length
		dataInRead = Math.Min(dataIn.Length, dataOut.Length);
		dataOutWritten = dataInRead;

		var readBytes = new byte[dataInRead];
		dataIn.Read(readBytes, 0, readBytes.Length);
		dataOut.Write(readBytes, 0, readBytes.Length);

		//If we read less than the total amount avaliable then we need
		//return FilterStatus.NeedMoreData so we can then write the rest
		if (dataInRead < dataIn.Length)
		{
			return FilterStatus.NeedMoreData;
		}

		return FilterStatus.Done;
	}

	public void Dispose()
	{

	}
}

See the CefSharp.Exampleproject within the source for additional example implementations of IResourceFilter. This feature is quite complex to implement. Make sure you read over and debug the existing examples before asking any questions.

Loading HTML/CSS/JavaScript/etc from disk/database/embedded resource/stream

There are a few extension methods provided as a convenience in the CefSharp.WebBrowserExtensions class.

//Load a data encoded Uri
//NOTE There are limits to the size of a Data Uri, use the overload that takes a Url if you need to load large files
LoadHtml(this IWebBrowser browser, string html, bool base64Encode = false);

//Register a ResourceHandler with the `ResourceRequestHandlerFactory` and calls browser.Load
LoadHtml(this IWebBrowser browser, string html, string url)`;

//Register a resource handler with the `ResourceRequestHandlerFactory`
RegisterResourceHandler(this IWebBrowser browser, string url, Stream stream, string mimeType = 
ResourceHandler.DefaultMimeType);

//Unregister a resource handler with the `ResourceRequestHandlerFactory`
UnRegisterResourceHandler(this IWebBrowser browser, string url);

//In `WinForms` you can pass a `HtmlString` directly into the constructor and have it load as a Data Uri
new ChromiumWebBrowser((CefSharp.Web.HtmlString)"<html><body style='background:red;'>Data Uri Test</body></html>");

For more information on data: encoded URI, which contains the body of the request in the URI itself see https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs

Generating your own Data URI would look something like:

const string html = "<html><head><title>Test</title></head><body><h1>Html Encoded in URL!</h1></body></html>";
var base64EncodedHtml = Convert.ToBase64String(Encoding.UTF8.GetBytes(html));
browser.Load("data:text/html;base64," + base64EncodedHtml);

Request Handling

RequestHandler and ResourceRequestHandler can be used to intercept network requests, add headers, add post data, read response headers, perform redirects, etc.

For loading resources from memory/disk/database see Resource Handling

The following provides an example of how to only allow loading of resources from a specific host.

public class CustomResourceRequestHandler : CefSharp.Handler.ResourceRequestHandler
{
	protected override CefReturnValue OnBeforeResourceLoad(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IRequestCallback callback)
	{
		if (Uri.TryCreate(request.Url, uriKind: UriKind.Absolute, out Uri result))
		{
			if (string.Compare(result.Host, "www.google.com", StringComparison.OrdinalIgnoreCase) == 0)
			{
				return CefReturnValue.Continue;
			}
		}

		return CefReturnValue.Cancel;

		//If you wanted to perform some sort of database lookup to validate the Url then you should use a Task for processing
		//System.Threading.Tasks.Task.Run(() =>
		//{
		//    using (callback)
		//    {
		//        if (Uri.TryCreate(request.Url, uriKind: UriKind.Absolute, out Uri uri))
		//        {
		//            //Query  Database here and confirm Url matches
		//            var validUrl = string.Compare(uri.Host, "www.google.com", StringComparison.OrdinalIgnoreCase) == 0;

		//            //Continue if it's a valid Url
		//            callback.Continue(validUrl);
		//        }
		//        else
		//        {
		//            //Failed to parse the Url, we'll cancel
		//            callback.Cancel();
		//        }
		//    }
		//});

		//return CefReturnValue.ContinueAsync;
	}
}

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		//Use our custom ResourceRequestHandler to hook OnBeforeResourceLoad
		return new CustomResourceRequestHandler();

		//For the default behaviour, return null
		//url will be loaded normally.
		//return null;
	}
}

browser.RequestHandler = new CustomRequestHandler();

File URI (file:///)

I strongly advise against using file:/// when loading from local disk. Different security restrictions apply and there are many limitations. I'd suggest using a Scheme handler or implementing your own IResourceRequestHandlerFactory. (Loading a data: encoded URI is also pretty handy, specially for the OffScreen project).

If you choose to ignore this advice you'll have to resolve any issues you have using file:/// yourself. ceforum is the best resource.

Proxy Resolution

There are two options for configuring a proxy server.

  1. CEF using the same command-line flags as Google Chrome.
  2. Proxy settings can be set/changed at runtime using IRequestContext.SetPreference
    • IRequestContext.SetPreference must be called on the CEF UI thread. Use Cef.UIThreadTaskFactory to spawn a task on the CEF UI Thread. IRequestContextHandler methods are already called on the CEF UI thread so you can call SetPreference directly. Alternatively call IRequestContext.SetPreferenceAsync which can be called on any Thread (will invoke onto the CEF UI Thread if required).
    • It is possible to specify the proxy settings on a per Request Context basis allowing you to have different ChromiumWebBrowser instances using different proxies.
    • Read the Request Context section below for more details and a basic code example.
//Create a new RequestContext that users a specific proxy server
//By default an in memory cache is used
var requestContext = RequestContext
	.Configure()
	.WithProxyServer("127.0.0.1", 8080)
	.Create();

//Create a RequestContext with a proxy and cache path
//Making sure that CachePath is equal to or a child of CefSettings.RootCachePath
//See https://github.com/cefsharp/CefSharp/issues/3111#issuecomment-629713608 for more info on cache path
var requestContext = RequestContext
	.Configure()
	.WithProxyServer("127.0.0.1", 8080)
	.WithCachePath(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache"))
	.Create();

//Set the proxy at runtime, the RequestContext must be initialized
Cef.UIThreadTaskFactory.StartNew(delegate
{
	string errorMessage;

	if (!requestContext.CanSetPreference("proxy"))
	{
		//Unable to set proxy, if you set proxy via command line args it cannot be modified.
	}

	success = requestContext.SetProxy("127.0.0.1", 8080, out errorMessage);
});

Some Additional examples of setting proxy using Preferences in CefSharp are available at http://stackoverflow.com/questions/36095566/cefsharp-3-set-proxy-at-runtime

Proxy Authentication

If the proxy requires authentication the IRequestHandler.GetAuthCredentials() method will be executed with an isProxy value of true to retrieve the username and password.

Example of providing UserName/Password for Proxy

browser.RequestHandler = new CustomRequestHandler();

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override bool GetAuthCredentials(IWebBrowser chromiumWebBrowser, IBrowser browser, string originUrl, bool isProxy, string host, int port, string realm, string scheme, IAuthCallback callback)
	{
		//Cast IWebBrowser to ChormiumWebBrowser if you need to access the UI control
		//You can Invoke onto the UI Thread if you need to show a dialog
		var b = (ChromiumWebBrowser)chromiumWebBrowser;

		if(isProxy)
		{
			using (callback)
			{
				callback.Continue(username: "user", password: "pass");
			}

			return true;
		}

		//Return false to cancel the request
		return false;
	}
}

Request Context (Browser Isolation)

You can isolate browser instances, including providing custom cache paths, different proxy settings, different cookie managers, and many other things using a RequestContext. In CEF terms the underlying class is CefRequestContext.

Here are some key points:

//WinForms Examples - WPF and OffScreen are similar, see notes above.

//Default implementation of RequestContext
//Default settings will be used, this means an in-memory cache (no data persisted)
browser = new ChromiumWebBrowser();
browser.RequestContext = new RequestContext();

// Use RequestContext.Configure to create a RequestContext using a 
// Fluent style interface, can be used to set proxy, set preferences, cachePath
// Use WithSharedSettings to share settings with another RequestContext
// This one will share the same CachePath as the Global RequestContext
var ctx = RequestContext.Configure()
                .WithSharedSettings(Cef.GetGlobalRequestContext())
                .WithPreference("webkit.webprefs.minimum_font_size", 24)
                .Create();

browser = new ChromiumWebBrowser("www.google.com");
browser.RequestContext = ctx;

//CustomRequestContextHanler needs to implement `IRequestContextHandler`
//Default settings will be used, this means an in-memory cache (no data persisted)
browser = new ChromiumWebBrowser();
browser.RequestContext = new RequestContext(new CustomRequestContextHandler());

//Custom settings and CustomRequestContextHandler
//Use the specified cache path (if empty, in memory cache will be used). To share the global
//browser cache and related configuration set this value to match the CefSettings.CachePath
//value.
var requestContextSettings = new RequestContextSettings { CachePath = cachePath };
browser = new ChromiumWebBrowser();
browser.RequestContext = new RequestContext(requestContextSettings, new CustomRequestContextHandler());

See the project source for more detailed examples.

//When you are already on the CEF UI Thread you can use the following
string errorMessage;
//You can set most preferences using a `.` notation rather than having to create a complex set of dictionaries.
//Disable resizing of text areas
//The default is true, you can change to false to disable
context.SetPreference("webkit.webprefs.text_areas_are_resizable", true, out errorMessage);
//Change the minimum font size to 24pt
context.SetPreference("webkit.webprefs.minimum_font_size", 24, out errorMessage);

//To execute on the CEF UI Thread you can use 
Cef.UIThreadTaskFactory.StartNew(delegate
{
    string errorMessage;
    //Use this to check that settings preferences are working in your code

    //the browser variable is an instance of ChromiumWebBrowser
    var success = browser.RequestContext.SetPreference("webkit.webprefs.minimum_font_size", 24, out errorMessage);
});

Setting preferences in OnRequestContextInitialized (this approach is recommended for setting a proxy as it will be called before the browser attempts to load any web page)

public class RequestContextHandler : CefSharp.Handler.RequestContextHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		// Return null for the default behaviour
		// Implement CefSharp.IResourceRequestHandler or inherit from CefSharp.Handler.ResourceRequestHandler
		// To handle resource requests at the RequestContext level

		return null;
	}

	protected override void OnRequestContextInitialized(IRequestContext requestContext)
	{
		//You can set preferences here on your newly initialized request context.
		//Note, there is called on the CEF UI Thread, so you can directly call SetPreference

		//Use this to check that settings preferences are working in your code
		//You should see the minimum font size is now 24pt
		string errorMessage;
		var success = requestContext.SetPreference("webkit.webprefs.minimum_font_size", 24, out errorMessage);

		//Set proxy to fixed_servers
		//Make sure to include using CefSharp; to access this extension method
		var setProxySuccess = requestContext.SetProxy("scheme", "host", port: 8080, out string error);

		//Alternatively you can set the proxy with code similar to the code below
		//https://stackoverflow.com/questions/36095566/cefsharp-3-set-proxy-at-runtime has some additional examples
		//var v = new Dictionary<string, object>
		//{
		//    ["mode"] = "fixed_servers",
		//    ["server"] = "scheme://host:port"
		//};
		//string errorMessage;
		//bool success = requestContext.SetPreference("proxy", v, out errorMessage);
	}
}

Printing

The CEF API only exposes limited support for printing. There is currently no support for printing in Kiosk Mode (printing to the default without a dialog). The suggested workaround is to print to PDF then use a 3rd party application to print the PDF.

If you need better printing support then you should discuss that on ceforum. There are already open discussions and an open issue on the CEF Issue Tracker.

High DPI Displays/Support

Desktop applications using WinForms/WPF need to be made DPI Aware to run correctly on a High DPI Display (A display with a DPI Scale set greater than 100%).

Note If you mouse cursor is incorrectly positioned in the browser or the browser displays black boxes/border with rendering/resizing then your app needs to be made DPI Aware. Other parts of your application may also appear blurry or incorrectly-sized.

There are a number of options used to configure the DPI awareness of a process:

  1. Through an application manifest setting (This is generally the preferred option)
  2. Via app.config (WinForms Only where targeting .Net 4.7 and above). IMPORTANT There is a mistake in the Microsoft documentation see https://github.com/dotnet/docs-desktop/issues/1485
  3. Programmatically through an API call. This is not recommended for WinForms or WPF.

Windows 10 1703 has additional improvements see https://blogs.windows.com/windowsdeveloper/2017/04/04/high-dpi-scaling-improvements-desktop-applications-windows-10-creators-update/ for more details.

WinForms High DPI

Starting with the .NET Framework 4.7, Windows Forms includes enhancements for common high DPI and dynamic DPI scenarios. In previous versions of the .NET Framework, you used the app.manifest to add high DPI support. This approach is no longer recommended, since it overrides settings defined on the app.config file. Make sure to read High DPI support in Windows Forms for further details from Microsoft. IMPORTANT There is a mistake in the Microsoft documentation see https://github.com/dotnet/docs-desktop/issues/1485

App.manifest

IMPORTANT If you are targeting .Net 4.7 or above Microsoft recommends configuring DPI Awareness via the app.config rather than app.manifest. Make sure to read High DPI support in Windows Forms for further details from Microsoft. IMPORTANT There is a mistake in the Microsoft documentation see https://github.com/dotnet/docs-desktop/issues/1485

Set the default awareness using the application manifest. The following example is PerMonitor DPI Aware on Win 10 1703 and above and PerMonitor DPI aware on older version. Make sure you read https://docs.microsoft.com/en-us/windows/win32/hidpi/high-dpi-desktop-application-development-on-windows#dpi-awareness-mode which discusses the different DPI Awareness options. If you project doesn't already have an app.manifest use the Visual Studio New Item template to add one rather than doing so manually to ensure the relevant <ApplicationManifest/> entry in your csproj/vbproj file is added (it's a special type).

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<application xmlns="urn:schemas-microsoft-com:asm.v3">
    <windowsSettings>
        <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
        <dpiAware>true/PM</dpiAware>
    </windowsSettings>
</application>
</assembly>

Programmatically

For WinForms use the app.config option if possible or app.manifest if using an older version. Setting DPI Awareness programatically is not reccomended.

WPF High DPI

App.manifest

Add the relevant entries see Turn on Windows level Per monitor DPI awareness in app.manifest for Microsoft recommendations.

For a working example see https://github.com/cefsharp/CefSharp/blob/cefsharp/103/CefSharp.Wpf.Example/app.manifest for a working example. If you project doesn't already have an app.manifest use the Visual Studio New Item template to add one rather than doing so manually to ensure the relevant <ApplicationManifest/> entry in your csproj/vbproj file is added (it's a special type).

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
<application xmlns="urn:schemas-microsoft-com:asm.v3">
    <windowsSettings>
        <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
        <dpiAware>true/PM</dpiAware>
    </windowsSettings>
</application>
</assembly>

Programmatically

WPF applications by default have an automatically generated Program.Main entry point which makes it harder to programmatically set the DPI. See https://stackoverflow.com/a/26890426/4583726 for how to create a Program.Main then you can call Cef.EnableHighDPISupport();. This must be called very early on in your application execution, preferably the first call in your custom Program.Main.

Using app.manifest is preferred.

OffScreen High DPI

Add the relevant app.manifest entries or call Cef.EnableHighDPISupport().

Programmatically

Setting High DPI in code you can use the Cef.EnableHighDPISupport(); helper method. This calls the Chromium base::win::EnableHighDPISupport(); function. You then have exactly the same settings as Chromium uses.

Cef.EnableHighDPISupport(); must be called very early on in your application execution, preferably in your application entry point (Program.Main).

High DPI Additional Info

Chromium by default performs all rendering in separate sub-process. Specifically the GPU Compositor needs to have a DPI Awareness that matches your main application. Currently the default used by the CefSharp.BrowserSubprocess.exe is Per Monitor DPI Aware. As a workaround use the disable-gpu-compositing command line arg and the DPI Awareness of your main application process will be used instead of the DPI Awareness specified by the GPU Process (which is used for GPU Compositing). Disabling GPU Compositing may have an impact on performance, when https://github.com/cefsharp/CefSharp/issues/2927 is complete it will be possible to programmatically set the DPI Awareness used by the CefSharp.BrowserSubprocess.exe

var settings = new CefSettings();
settings.CefCommandLineArgs.Add("disable-gpu-compositing");
Cef.Initialize(settings);

Alternatively you can try the force-device-scale-factor command line flag. This should only be used in conjunction with the WinForms implementation.

var settings = new CefSettings();
settings.CefCommandLineArgs.Add("force-device-scale-factor", "1");
Cef.Initialize(settings);

MultiThreadedMessageLoop

CefSharp by default uses setting.MultiThreadedMessageLoop = true. This enables your application to get up and running very quickly, there are some important things to note and this may not be suitable for everyone.

  • Uses a different thread for the message pump.
  • The CEF UI thread is different to your application's UI thread, which can cause some disconnects in message processing.
    • One example is opening a menu and clicking within the browser control with the menu staying open.
  • Low level Win32 messages don't propagate between CEF and WinForms

It is possible to integrate CEF into your app's existing message loop. A very minimal implementation of integrating CEF into your existing message loop involves using a timer that's called 30/60 times per second on the UI thread.

var settings = new CefSettings();
settings.MultiThreadedMessageLoop = false; //This defaults to true

Cef.Initialize(settings);

- For WPF use [DispatcherTimer](https://docs.microsoft.com/en-us/dotnet/api/system.windows.threading.dispatchertimer?view=netframework-4.8)
- For WinForms use [Timer](https://docs.microsoft.com/en-us/dotnet/api/system.windows.forms.timer?view=netframework-4.8)

//Set the timer Interval to 30 times per second, can be increased to 60 if required
//For WPF
timer.Interval = TimeSpan.FromMilliseconds(1000 / 30);
//For WinForms
timer.Interval = 1000 / 30;
timer.Tick += UiThreadTimerTick;
timer.Start();

//Before closing your app
//Calling Cef.DoMessageLoopWork() after Cef.Shutdown has been called will result in
//an access violation, make sure you stop you timer first.
timer.Tick -= UiThreadTimerTick;
timer.Stop();

private void UiThreadTimerTick(object sender, EventArgs e)
{
    //Must be called on the UI Thread.
    Cef.DoMessageLoopWork();
}

A more advanced option involves setting CefSettings.ExternalMessagePump = true; and implementing IBrowserProcessHandler.OnScheduleMessagePumpWork. This allows CEF to notify when it needs to perform work, in some instances this may make your application more responsive. See https://github.com/cefsharp/CefSharp/issues/1748 for additional details. There are more advanced/working examples contained within the projects source.

You can hook the message loop whilst using MultiThreadedMessageLoop, though this is quite complex. The project source contains an example at https://github.com/cefsharp/CefSharp/blob/v53.0.0/CefSharp.WinForms.Example/BrowserTabUserControl.cs#L224 You can use this method to obtain Win32 mouse messages.

Popups

A common request is to control popup creation. Implement ILifeSpanHandler.OnBeforePopup to control how popups are created. To cancel popup creation altogether simply return true;. You can use the default LifeSpanHandler implemention to avoid implementing the whole interface.

chromiumWebBrowser.LifeSpanHandler = new LifeSpanHandler();

public class LifeSpanHandler : CefSharp.Handler.LifeSpanHandler
{
	protected override bool OnBeforePopup(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, string targetUrl, string targetFrameName, WindowOpenDisposition targetDisposition, bool userGesture, IPopupFeatures popupFeatures, IWindowInfo windowInfo, IBrowserSettings browserSettings, ref bool noJavascriptAccess, out IWebBrowser newBrowser)
	{
		newBrowser = null;
		
		//Return true to cancel the popup creation
		return true;
	}
}

You can cancel popup creation and open targetUrl in a new ChromiumWebBrowser instance. It is important to note the parent-child relationship will not exist using this method. So in general it's not recommended.

WinForms - Hosting Popup using TAB Control

For WinForms you can use the build in LifeSpanHandler implementation to host a popup browser as a TAB.

browser.LifeSpanHandler = CefSharp.WinForms.Handler.LifeSpanHandler
	.Create()
	.OnPopupCreated((ctrl, targetUrl) =>
	{
		//Add popup to new parent control e.g. Tab
		parent.Controls.Add(ctrl);
	})
	.OnPopupDestroyed((ctrl, popupBrowser) =>
	{
		//If browser is disposed or the handle has been released then we don't
		//need to remove the tab (likely removed from menu)
		if (!ctrl.IsDisposed && ctrl.IsHandleCreated)
		{
			parent.Controls.Remove(ctrl);
		}
	}).Build();

WPF - Hosting Popup in new Window (EXPERIMENTAL)

Starting in M107 there is an experimental LifeSpanHandler implementation for hosting the popup using a ChromiumWebBrowser instance Allows you to host the popup using the newBrowser param in OnBeforePopup in WPF. There are some known UPSTREAM issues with this approach and will need to be fixed in CEF.

// Open popup (browser) in a new WPF Window
// Can be used to host in TabControl/ContentControl/etc
browser.LifeSpanHandler = CefSharp.Wpf.Experimental.LifeSpanHandler
	.Create()
	.OnPopupCreated((ctrl, targetUrl, targetFrameName, windowInfo) =>
	{
		// Called on the WPF UI Thread
		// Now is the prefferred time to attach ctrl (ChormiumWebBrowser)
		// to it's parent
	})
	.OnPopupDestroyed((ctrl, popupBrowser) =>
	{
	    // Remove ctrl (ChormiumWebBrowser) from Visual Tree
		// Called on the WPF UI Thread
		
	}).Build();

JavaScript Integration

1. How do you call a JavaScript method from .NET?

Simple code may look something like this:

//There are a number of extension methods that simplify execution, they all work on the main frame
//They all exists in the CefSharp.WebBrowserExtensions class, make sure you add "using CefSharp;"
browser.ExecuteScriptAsync("document.body.style.background = 'red';");

// When executing multiple statements, group them together in an IIFE
// https://developer.mozilla.org/en-US/docs/Glossary/IIFE
// For Google.com pre-populate the search text box and click the search button
browser.ExecuteJavaScriptAsync("(function(){ document.getElementsByName('q')[0].value = 'CefSharp Was Here!'; document.getElementsByName('btnK')[0].click(); })();");

If you have a web page with multiple frames you can execute the script on the sub frames

browser.GetBrowser().GetFrame("SubFrame").ExecuteJavaScriptAsync("document.body.style.background = 'red';");

When can I start executing JavaScript?

JavaScript can only be executed within a V8Context. The IRenderProcessMessageHandler.OnContextCreated and IRenderProcessMessageHandler.OnContextReleased provide a boundary for when JavaScript can be executed. OnContextCreated/OnContextReleased will be called once per frame, use frame.IsMain to check for the main frame.

It's tempting to start trying to access the DOM in OnFrameLoadStart, whilst the V8Context will have been created and you will be able to execute a script the DOM will not have finished loading. If you need to access the DOM at it's earliest possible point then subscribe to DOMContentLoaded, some examples of executing JavaScript are below.

browser.RenderProcessMessageHandler = new RenderProcessMessageHandler();

public class RenderProcessMessageHandler : IRenderProcessMessageHandler
{
  // Wait for the underlying JavaScript Context to be created. This is only called for the main frame.
  // If the page has no JavaScript, no context will be created.
  void IRenderProcessMessageHandler.OnContextCreated(IWebBrowser browserControl, IBrowser browser, IFrame frame)
  {
    const string script = "document.addEventListener('DOMContentLoaded', function(){ alert('DomLoaded'); });";

    frame.ExecuteJavaScriptAsync(script);
  }
}

//Wait for the page to finish loading (all resources will have been loaded, rendering is likely still happening)
browser.LoadingStateChanged += (sender, args) =>
{
  //Wait for the Page to finish loading
  if (args.IsLoading == false)
  {
    browser.ExecuteJavaScriptAsync("alert('All Resources Have Loaded');");
  }
}

//Wait for the MainFrame to finish loading
browser.FrameLoadEnd += (sender, args) =>
{
  //Wait for the MainFrame to finish loading
  if(args.Frame.IsMain)
  {
    args.Frame.ExecuteJavaScriptAsync("alert('MainFrame finished loading');");
  }
};

Some notes about executing JavaScript:

  • Scripts are executed at the frame level, and every page has at least one frame (MainFrame).
  • The IWebBrowser.ExecuteScriptAsync extension method is left for backwards compatibility, you can use it as a shortcut to execute js on the main frame.
  • If a frame does not contain JavaScript then no V8Context will be created.
  • For a frame that doesn't have a context executing a script once the frame has loaded it's possible to create a V8Context using IFrame.ExecuteJavaScriptAsync.
  • The DOM won't have finished loading when OnFrameLoadStart is fired
  • IRenderProcessMessageHandler.OnContextCreated/OnContextReleased are only called for the main frame.

2. How do you call a JavaScript method that returns a result?

If you need to call(evaluate) JavaScript which returns a value, use one of the following:

//An extension method that evaluates JavaScript against the main frame.
JavascriptResponse response = await browser.EvaluateScriptAsync(script);
//Evaluate javascript directly against a frame
JavascriptResponse response = await frame.EvaluateScriptAsync(script);

//An extension method that evaluates Javascript Promise against the main frame.
//Uses Promise.resolve to return the script execution into a promise regardless of the return type
//This method differs from EvaluateScriptAsync in that your script **must return** a value
//Examples below
JavascriptResponse response = await browser.EvaluateScriptAsPromiseAsync(script);

JavaScript code is executed asynchronously and as such returns Task which contains error message, result and a success (bool) flag. Here are the fundamentals you need to know when evaluating JavaScript

  • Please make sure you read When can I start executing JavaScript?.
  • Scripts are executed at the Frame level, and every page has at least one frame (MainFrame).
  • Scripts are executed in the render process and are transmitted via IPC, return only the data you require for performance reasons.
  • Primitive data types int, double, date, bool and string are supported.
  • Objects are supported to a degree and will be returned as IDictionary<string, object>, the use of the dynamic keyword is supported to make accessing the property values easier.
  • You cannot directly return a DOM Element (or anything with a cyclic reference), you need to create a new object that has just the information you need to return.
  • Arrays containing the primitives listed above and objects are supported and will be returned as IList<object>.
  • Array Like objects like HTMLCollection cannot be returned directly use Array.from to return and array
  • There are limits to the complexity of the object graph that can be returned (graphs with cyclic references aren't supported currently), in these cases you may need to turn the JavaScript object into a JSON string with the JavaScript JSON.stringify() method and return that string to your .NET code. Then you can decode that string into a .NET object with something like JSON.NET. See MDN JSON.stringify for more details. See https://stackoverflow.com/a/46881092/4583726 for some guidence on using JSON.stringify with HTMLElement.
//Start with something simple, the following will return the value 2 as type int
//Don't use the `return` keyword
//chromiumWebBrowser.EvaluateScriptAsync executes on the main frame, scripts can be executed
//per frame if required
JavascriptResponse response = await frame.EvaluateScriptAsync("1 + 1");
JavascriptResponse response = await chromiumWebBrowser.EvaluateScriptAsync("1 + 1");

var onePlusOne = (int)response.Result;

//A javascript IFFE will be evaluated and it's result returned.
//https://developer.mozilla.org/en-US/docs/Glossary/IIFE
//If you want to execute multiple lines of javascript then an IIFE is recommended to
//avoid any variable scoping issues
var script = @"(function() { let val = 1 + 1; return val; })();";
JavascriptResponse response = await frame.EvaluateScriptAsync(script);

var onePlusOne = (int)response.Result;

//If your script uses a Promise then you must use the EvaluateScriptAsPromiseAsync method, it differs slightly
//in that you must return the value.
//The following will return a Promise that after one second resolves with a simple objec
var script = "return new Promise(function(resolve, reject) { setTimeout(resolve.bind(null, { a: 'CefSharp', b: 42, }), 1000); });"
JavascriptResponse javascriptResponse = await browser.EvaluateScriptAsPromiseAsync(script);
//You can access the object using the dynamic keyword for convenience.
dynamic result = javascriptResponse.Result;
var a = result.a;
var b = result.b;

//EvaluateScriptAsPromiseAsync calls Promise.resolve internally so even if your code doesn't
//return a Promise it will still execute successfully.
var script = @"return (function() { return 1 + 1; })();";
JavascriptResponse response = await frame.EvaluateScriptAsPromiseAsync(script);

// An example that gets the Document Height
var task = frame.EvaluateScriptAsync("(function() { var body = document.body, html = document.documentElement; return  Math.max( body.scrollHeight, body.offsetHeight, html.clientHeight, html.scrollHeight, html.offsetHeight ); })();");

//Continue execution on the UI Thread
task.ContinueWith(t =>
{
    if (!t.IsFaulted)
    {
        var response = t.Result;
        EvaluateJavaScriptResult = response.Success ? (response.Result ?? "null") : response.Message;
    }
}, TaskScheduler.FromCurrentSynchronizationContext());

//HTMLElement/HTMLCollection Examples
//As stated above, you cannot return a HTMLElement/HTMLCollection directly.
//It's best to return only the data you require, here are some examples of using Array.from to convert a HTMLCollection  into an array of objects
//which can be returned to your .Net application.

//Get all the span elements and create an array that contains their innerText
var script = @"Array.from(document.getElementsByTagName('span')).map(x => ( x.innerText));";
JavascriptResponse response = await frame.EvaluateScriptAsync(script);

//Get all the a tags and create an array that contains a list of objects 
//Second param is the mapping function
var script = @"Array.from(document.getElementsByTagName('a'), x => ({ innerText : x.innerText, href : x.href }));";
JavascriptResponse response = await frame.EvaluateScriptAsync(script);

//List of Links, click represents a function pointer which can be used to execute the link click)
//In .Net the https://cefsharp.github.io/api/118.6.x/html/T_CefSharp_IJavascriptCallback.htm is used
//to represent the function.
var script = @"Array.from(document.getElementsByTagName('a')).map(x => ({ innerText: x.innerText, click: x.click}));";
JavascriptResponse response = await frame.EvaluateScriptAsync(script);

//Execute the following against google.com to get the `I'm Feeling Lucky` button then click the button in .Net
//NOTE: This is a simple example, you could return an aggregate object consisting of data from multiple html elements.
const string script = @"(function()
{
  let element = document.getElementsByName('btnI')[0];
  let obj = {};
  obj.id = element.id;
  obj.nodeValue = element.nodeValue;
  obj.localName = element.localName;
  obj.tagName = element.tagName;
  obj.innerText = element.innerText;
  obj.click = element.click;
  obj.attributes = Array.from(element.attributes).map(x => ({name: x.name, value: x.value}));

  return obj;
})();";

var javascriptResponse = await chromiumWebBrowser.EvaluateScriptAsync(script);
dynamic result = javascriptResponse.Result;
var clickJavascriptCallback = (IJavascriptCallback)result.click;
await clickJavascriptCallback.ExecuteAsync();
//Dispose of the click callback when done
clickJavascriptCallback.Dispose();

//Get all rows/cells for the first table in the DOM
//dynamic can be used in c# to simplify accessing the result
var response = await chromiumWebBrowser.EvaluateScriptAsync(@"(function (){
	let srcTable = document.getElementsByTagName('table')[0];
	return Array.from(srcTable.rows, row => Array.from(row.cells, cell => cell.innerText));
	})();
");

dynamic arr = response.Result;

foreach(dynamic row in arr)
{
	foreach(var cell in row)
	{
		var data = (string)cell;
	}
}

Additional examples see Gist

3. How do you expose a .NET class to JavaScript?

JavaScript Binding (JSB) allows for communication between JavaScript and .Net. There are two distinct implementations available currently, the Async version and the older Sync version. The Sync version is no longer being actively developed, it relies on WCF which is not available in .Net Core or the upcoming .Net 5.0.

Async JavaScript Binding (JSB)

Summary

  • Uses Native Chromium IPC to pass messages back and forth between the Browser Process and Render Process., and as such is very fast.

  • Only methods are supported as the Native Chromium IPC is message based and can only be used in an async fashion (Property get/sets cannot be done in an async fashion)

  • Methods can return simple objects, structs and classes are supported, only a copy of the Properties is transferred to JavaScript. Think of it like making a webservice/ajax call, you get a response object.

  • Supports JavaScript callbacks, through the IJavascriptCallback

  • All method calls are non blocking and return a standard JavaScript Promise that can be awaited.

  • Method names are transformed to CamelCase (the first letter is transformed to lowercase, MyFunction becomes myFunction) by default. This is configurable by setting browser.JavascriptObjectRepository.NameConverter property before registering your objects, set to null to disable name conversion, detailed example below.

  • JavaScript Binding API details the different methods available.

  • Exceptions in .Net are caught and the Promise will be rejected.

  • See the Advanced Async JavaScript Binding (JSB) Wiki, please make sure you finish reading this first.

If you are not familiar with all Chromium has to offer when it comes to async programming here are some very useful articles

Binding an Async object in JavaScript

The CefSharp.BindObjectAsync method is called in Javascript to bind an object. CefSharp.BindObjectAsync returns a Promise that is resolved when bound object(s) are available. Objects are created in the global context (properties of the window object). If you call CefSharp.BindObjectAsync without any params then all registered objects will be bound. Binding by name is the more descriptive options.

The simple workflow would look like:

  • Step 1 Create a class that you wish to expose to javascript (don't use your Form/Window or Control)
  • Step 2 Register an instance of your class with the JavaScriptObjectRepository
  • Step 3 Call CefSharp.BindObjectAsync with the name of the object you wish to register, e.g. CefSharp.BindObjectAsync("boundAsync"); (Objects will only be available after the Promise has resolved.

Only Methods are supported. If you need to set a property, then create Get/Set methods.

Step 1 Create a class

A simple class would look like this:

public class BoundObject
{
    public int Add(int a, int b)
    {
        return a + b;
    }
}

Step 2 Register an instance of your class with the JavaScriptObjectRepository

The second part of the process is registering the object with the JavascriptObjectRepository (accessible though the browser.JavascriptObjectRepository property). You have two options for registering an object in .Net, the first is registered in advance, this is usually done immediately after you create a ChromiumWebBrowser instance. The second options is more flexible and allows objects to be Resolved when required.

First Option:

//For async object registration (equivalent to the old RegisterAsyncJsObject)
browser.JavascriptObjectRepository.Register("boundAsync", new BoundObject(), true, BindingOptions.DefaultBinder);

Second Option (Preferred):

browser.JavascriptObjectRepository.ResolveObject += (sender, e) =>
{
	var repo = e.ObjectRepository;
	if (e.ObjectName == "boundAsync")
	{
		BindingOptions bindingOptions = null; //Binding options is an optional param, defaults to null
		bindingOptions = BindingOptions.DefaultBinder //Use the default binder to serialize values into complex objects
		bindingOptions = new BindingOptions { Binder = new MyCustomBinder() }); //Specify a custom binder
		repo.NameConverter = null; //No CamelCase of Javascript Names
		//For backwards compatability reasons the default NameConverter doesn't change the case of the objects returned from methods calls.
		//https://github.com/cefsharp/CefSharp/issues/2442
		//Use the new name converter to bound object method names and property names of returned objects converted to camelCase
		repo.NameConverter = new CamelCaseJavascriptNameConverter();
		repo.Register("boundAsync", new BoundObject(), isAsync: true, options: bindingOptions);
	}
};

To be notified in .Net when objects have been bound in JavaScript then you can subscribe to ObjectBoundInJavascript event or the ObjectsBoundInJavascript event (both events are very similar obviously).

browser.JavascriptObjectRepository.ObjectBoundInJavascript += (sender, e) =>
{
	var name = e.ObjectName;

	Debug.WriteLine($"Object {e.ObjectName} was bound successfully.");
};

Step 3 Call CefSharp.BindObjectAsync

<script type="text/javascript">
(async function()
{
	await CefSharp.BindObjectAsync("boundAsync");
	
	//The default is to camel case method names (the first letter of the method name is changed to lowercase)
	boundAsync.add(16, 2).then(function (actualResult)
	{
		const expectedResult = 18;
		assert.equal(expectedResult, actualResult, "Add 16 + 2 resulted in " + expectedResult);
	});
})();

When a CefSharp.BindObjectAsync call is made, the JavascriptObjectRepository is queried to see if an object with the given name is already registered, if no matching object is found then the ResolveObject event is raised. For calls to CefSharp.BindObjectAsync without any params, then if objects have already been registered then they will all be bound, if no objects have been registered then ResolveObject will be called with the ObjectName set to All.

Only the basics are covered in this section, there are many advanced options check out Advanced Async Javascript Binding

If you'd like to see a working example then checkout CefSharp MinimalExample Javascript Binding Demo branch, specifically commit

Sync JavaScript Binding (JSB)

THIS IS A LEGACY FEATURE - anyone creating a new application use the Async JavaScript Binding (JSB) implementation as it's under active development. The Sync version will only receive bug fixes for regressions.

  • Uses a WCF service for communication (Microsoft have not included support for WCF in .Net Core/.Net 5.0, there's no long term future for WCF).
  • Supports both methods and properties
  • Calls are executed in a sync fashion and are blocking, long running calls will block the Render Process and make your app appear slow or become unresponsive.
  • Supports semi complex object structures
  • Occasionally the WCF service doesn't shutdown cleanly and slows down application shutdown
Binding an object in JavaScript

Binding is initiated by JavaScript, the CefSharp.BindObjectAsync method returns a Promise that is resolved when bound objects are available. Objects are created in the global context (properties of the window object). If you call CefSharp.BindObjectAsync without any params then all registered objects will be bound. Binding by name is the more descriptive options.

The simple workflow would look like:

  • Step 1 Create a class that you wish to expose to JavaScript (don't use your Form/Window or Control)
  • Step 2 Call CefSharp.BindObjectAsync with the name of the object you wish to register, e.g. CefSharp.BindObjectAsync("myObject"); (Objects will only be available after the Promise has resolved.
  • Step 3 Register your object with the JavaScriptObjectRepository

Step 1

public class BoundObject
{
    public string MyProperty { get; set; }
    public void MyMethod()
    {
        // Do something really cool here.
    }
    
    public void TestCallback(IJavascriptCallback javascriptCallback)
    {
        const int taskDelay = 1500;

        Task.Run(async () =>
        {
            await Task.Delay(taskDelay);

            using (javascriptCallback)
            {
                //NOTE: Classes are not supported, simple structs are
                var response = new CallbackResponseStruct("This callback from C# was delayed " + taskDelay + "ms");
                await javascriptCallback.ExecuteAsync(response);
            }
        });
    }
}

Step 2 Call CefSharp.BindObjectAsync, Some examples below of Binding an object look like:

NOTE This is a two part process, see below the examples for details

<script type="text/javascript">
(async function()
{
	await CefSharp.BindObjectAsync("boundAsync");
	
	boundAsync.div(16, 2).then(function (actualResult)
	{
		const expectedResult = 8
		assert.equal(expectedResult, actualResult, "Divide 16 / 2 resulted in " + expectedResult);
	});
	
	boundAsync.error().catch(function (e)
    	{
        	var msg = "Error: " + e + "(" + Date() + ")";
    	});
})();

(async () =>
{
	await CefSharp.BindObjectAsync("boundAsync");
	
	boundAsync.hello('CefSharp').then(function (res)
	{
		assert.equal(res, "Hello CefSharp")
	});
})();

CefSharp.BindObjectAsync("boundAsync2").then(function(result)
{
	boundAsync2.hello('CefSharp').then(function (res)
	{
		assert.equal(res, "Hello CefSharp")
                // NOTE the ability to delete a bound object
		assert.equal(true, CefSharp.DeleteBoundObject("boundAsync2"), "Object was unbound");
		assert.ok(window.boundAsync2 === undefined, "boundAsync2 is now undefined");
	});
});
</script>

Step 3

The second part of the process is registering the object with the JavascriptObjectRepository (accessible though the browser.JavascriptObjectRepository property). You have two options for registering an object in .Net, the first is registered in advance, this is usually done immediately after you create a ChromiumWebBrowser instance. The second options is more flexible and allows objects to be Resolved when required.

When a CefSharp.BindObjectAsync call is made, the JavascriptObjectRepository is queries to see if an object with the given name is specified is already registered, if no matching object is found then the ResolveObject event is raised. For calls to CefSharp.BindObjectAsync without any params, then if objects have already been registered then they will all be bound, if no objects have been registered then ResolveObject will be called with the ObjectName set to All.

//When a 
browser.JavascriptObjectRepository.ResolveObject += (sender, e) =>
{
	var repo = e.ObjectRepository;
	if (e.ObjectName == "boundAsync2")
	{
		BindingOptions bindingOptions = null; //Binding options is an optional param, defaults to null
		bindingOptions = BindingOptions.DefaultBinder //Use the default binder to serialize values into complex objects,
		bindingOptions = new BindingOptions { Binder = new MyCustomBinder() }); //No camelcase of names and specify a custom binder
		//For backwards compatability reasons the default NameConverter doesn't change the case of the objects returned from methods calls.
		//https://github.com/cefsharp/CefSharp/issues/2442
		//Use the new name converter to bound object method names and property names of returned objects converted to camelCase
		repo.NameConverter = new CamelCaseJavascriptNameConverter();
		repo.Register("bound", new BoundObject(), isAsync: false, options: bindingOptions);
	}
};

In the actual JS code, you would use the object like this (default is to CamelCase Javascript Names, this is controllable via JavascriptObjectRepository.NameConverter, see above for an example).

bound.myProperty; // use this syntax to access the property
bound.myMethod(); // use this to call the method.
bound.testCallback(callback); //Pass a function in to use as a callback

Please note:

  • DO NOT REGISTER YOUR FORM/WINDOW/CONTROL. Create a class and proxy calls if required.
  • By default, methods and properties are changed into camelCase (i.e. the first letter is lower-cased) to make its usage be natural in JavaScript code. To disable set browser.JavascriptObjectRepository.NameConverter to null
  • Complex objects are supported for properties (where applicable) so you can now do bound.subObject.myFunction() and bound.subObject.myProperty = 1.
  • Complex object support for functions is now possible thorugh the IBinder interface, you can implement your own or use the DefaultBinder e.g. repo.Register("bound", new BoundObject(), BindingOptions.DefaultBinder);

RegisterAsyncJsObject

This method has been removed. See Async JavaScript Binding (JSB) instead.

RegisterJsObject

This has been removed. See Sync JavaScript Binding (JSB) instead.

Adobe Flash Player (Pepper Flash)

NOTE: Flash is now deprecated and Chromium has removed support, see https://www.chromium.org/flash-roadmap#TOC-Upcoming-Changes for further details.

Offscreen Rendering (OSR)

The WPF and OffScreen versions use the OffScreen Rendering (OSR) rendering mode. In OSR mode each frame is rendered to a buffer and then either drawn on the screen as in the case of WPF, or made available as a Bitmap in the OffScreen.

WPF

For the WPF control, user input (mouse clicks/moves and key presses) is forwarded to the underlying browser though methods on the IBrowserHost interface. It is possible to obtain access to each Bitmap as it's rendered.

A special note should be made about hosting the ChromiumWebBrowser within a ViewBox. This is far from ideal, as every frame is rendered then post-processing happens to resize/scale the image. This is a huge performance hit and often reduces quality (it's usually quite blurry). You can adjust the resize quality using RenderOptions.SetBitmapScalingMode. It's best to avoid using a ViewBox. You can scale the content contained within the browser by adjusting the ZoomLevel, which is by far the most performant option.

OffScreen

For the CefSharp.OffScreen package, each frame is rendered to a Bitmap and exposed for use. If you wish to interact with the browser via keyboard or mouse, you can use methods on the IBrowser host interface. Simulating key presses and mouse clicks/moves can be quite complex. You can use the WPF control as a starting example as it uses the same methods (add debugging to see what sequence of events is required). Key presses and mouse clicks/moves are often made up of multiple parts, up/down with a number of other possible combinations.

UserAgent

  1. You can specify a custom UserAgent by setting the CefSettings.UserAgent property. This change is applied globally and will be the default for all browser instances.
var settings = new CefSettings();
settings.UserAgent = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36 - Testing 123";
Cef.Initialize(settings);
  1. Starting with version 85, the UserAgent can be changed at runtime using the DevTools protocol.
using (var client = chromiumWebBrowser.GetDevToolsClient())
{
	_ = client.Network.SetUserAgentOverrideAsync("Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36 - Testing 123");
}

To change the UserAgent at runtime before the browser has made it's first request see https://gist.github.com/amaitland/0b05701710064203171bfd05f5002514#file-setuseragentoverrideasync-cs for an example.

  1. You can modify the User-Agent HTTP header in IResourceRequestHandler.OnBeforeResourceLoad, which would need to be done for every request. What it doesn't do is change the UserAgent the browser reports to JavaScript.
public class CustomResourceRequestHandler : CefSharp.Handler.ResourceRequestHandler
{
	protected override CefReturnValue OnBeforeResourceLoad(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IRequestCallback callback)
	{
		//Set the header by name, override the existing value
		request.SetHeaderByName("user-agent", "MyBrowser CefSharp Browser", true);

		return CefReturnValue.Continue;
	}
}

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		//Where possible only intercept specific Url's
		//Load https://www.whatismybrowser.com/detect/what-is-my-user-agent in the browser and you'll
		//see our custom user agent
		if (request.Url == "https://www.whatismybrowser.com/detect/what-is-my-user-agent")
		{
			return new CustomResourceRequestHandler();
		}

		//Default behaviour, url will be loaded normally.
		return null;
	}
}

browser.RequestHandler = new CustomRequestHandler();

DevTools

The Chromium DevTools are available for debugging Javascript, you can load DevTools programatically using the chromiumWebBrowser.ShowDevTools() method (there is a corresponding chromiumWebBrowser.CloseDevTools() method also). Make sure to add using CefSharp; to your usings statements. If you are new to DevTools check out the official Chrome guide.

Make sure you call this after the browser has been initialized.

using CefSharp;

//**OffScreen**
browser.BrowserInitialized += (sender, args) =>
{
    browser.ShowDevTools();
};

using CefSharp;

//**WinForms**
browser.IsBrowserInitializedChanged += (sender, args) =>
{
    browser.ShowDevTools();
};

//**WinForms (alternative)**
// If you see the DevTools window flickering 
// it's likely vying for focus with your form
// open DevTools on your UI Thread.
using CefSharp;

browser.IsBrowserInitializedChanged += (sender, args) =>
{
    var browser = (ChromiumWebBrowser)sender;

    browser.BeginInvoke((Action)delegate
    {
	    browser.ShowDevTools();
    });
};

using CefSharp;
//**WPF**
browser.IsBrowserInitializedChanged += (sender, args) =>
{
    if ((bool)args.NewValue)
    {
        browser.ShowDevTools();
    }
};

Alternatively you can connect Chrome to a running instance.

var settings = new CefSettings();
settings.RemoteDebuggingPort = 8088;
Cef.Initialize(settings);

Open http://localhost:8088 in Chrome.

Screenshots

You can capture a screenshot using the DevTools protocol, both PNG (default) and JPG formats are supported. This approach can be used in the WinForms/WPF/OffScreen versions.

The example below shows capturing with default settings. Additionally you can specify viewport size, quality, and other options.

//Make sure to dispose of our observer registration when done
//If you need to make multiple calls then reuse the devtools client
//and Dispose when done.
using (var devToolsClient = chromiumWebBrowser.GetDevToolsClient())
{
	var result = await devToolsClient.Page.CaptureScreenshotAsync();

	return result.Data;
}

The example below queries the current size of the content and captures currently rendered content. Note: Pages that delay load their content will need to be forced to render before you can take a whole page screenshot.

using (var devToolsClient = chromiumWebBrowser.GetDevToolsClient())
{
	//Get the content size
	var layoutMetricsResponse = await devToolsClient.Page.GetLayoutMetricsAsync();
	var contentSize = layoutMetricsResponse.ContentSize;

	var viewPort = new Viewport()
	{
		Height= contentSize.Height,
		Width = contentSize.Width,
		X = 0,
		Y = 0,
		Scale = 1 
	};

	// https://bugs.chromium.org/p/chromium/issues/detail?id=1198576#c17
	var result = await devToolsClient.Page.CaptureScreenshotAsync(clip: viewPort, fromSurface:true, captureBeyondViewport: true);

	return result.Data;
}

Additionally the DevTools protocol can be used to stream frames using Page.screencastFrame. Page Domain API doc for methods/events currently avaliable.

OffScreen/WPF

Both Offscreen and WPF use Offscreen Rendering (OSR) where every frame is rendered to a bitmap. It is still a web browser under the hood and not particularly well suited for this scenario. Here are some notes:

  • Lower frame rate, to make it easier to capture frames may be worth considering
  • You'll need to wait a period of time after the page has finished loading to allow the browser to render
  • There is currently no method of determining when a web page has finished rendering (and unlikely ever will be as with features like flash, dynamic content, animations, even simple tasks like moving your mouse or scrolling will cause new frames to be rendered).
  • A hack method to determine when rendering has approximately finished is to have a timer that's reset every time a frame is rendered, when no additional frames are rendered then the timer will file (not ideal)

WinForms

See example above

Win32 Out of Memory

When using the 32bit version make sure your application is large address aware (handle addresses larger than 2gb)

As per suggestion in http://magpcss.org/ceforum/viewtopic.php?f=6&t=15120#p34802 it appears that setting The Large Address Aware linker setting on your application executable when running as a 32bit application may now be necessary where high memory load is experienced.

The default x86 SubProcess shipped with CefSharp is large address aware, you should make your application large address aware as well.

After applying the Large Address Aware linker setting to your executable, if your still experiencing the exact same problem then discuss your issue at http://magpcss.org/ceforum/viewtopic.php?f=6&t=15120

Load URL with PostData

There are two methods for Loading a Url with Post Data, the first is to modify an existing Request. In the example below we'll add post data to the Request if we visit http://httpbin.org/post

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override IResourceRequestHandler GetResourceRequestHandler(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool isNavigation, bool isDownload, string requestInitiator, ref bool disableDefaultHandling)
	{
		//Where possible only intercept specific Url's
		//Load http://httpbin.org/post in the browser and you'll
		//see the post data
		if (request.Url == "http://httpbin.org/post")
		{
			return new CustomResourceRequestHandler();
		}

		//Default behaviour, url will be loaded normally.
		return null;
	}
}

public class CustomResourceRequestHandler : CefSharp.Handler.ResourceRequestHandler
{
	protected override CefReturnValue OnBeforeResourceLoad(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, IRequestCallback callback)
	{
				//Modify the request to add post data
		//Make sure to read https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
		var postData = new PostData();

		postData.AddData("test=123&data=456");

		request.Method = "POST";
		request.PostData = postData;
		//Set the Content-Type header to whatever suites your requirement
		request.SetHeaderByName("Content-Type", "application/x-www-form-urlencoded", true);
		//Set additional Request headers as required.

		return CefReturnValue.Continue;
	}
}

//Load http://httpbin.org/post in the browser to see the post data
browser = new ChromiumWebBrowser("http://httpbin.org/post");
browser.RequestHandler = new CustomRequestHandler();

The second method is to use IFrame.LoadRequest, this method can only be used if you have first successfully performed to a domain of the same origin. For example, you must navigate to say http://httpbin.org/ before you can call IFrame.LoadRequest for http://httpbin.org/post.

public void LoadCustomRequestExample()
{
	var frame = browser.GetMainFrame();

	//Create a new request knowing we'd like to use PostData
	var request = frame.CreateRequest(initializePostData:true);
	request.Method = "POST";
	request.Url = "http://httpbin.org/post";
        //Set AllowStoredCredentials so cookies are sent with Request
        request.Flags = UrlRequestFlags.AllowStoredCredentials;
	request.PostData.AddData("test=123&data=456");

	frame.LoadRequest(request);
}

The browser.LoadUrlWithPostData extension method can be used for simple cases, it calls LoadRequest and the same restrictions regarding having performed a successful navigation apply.

Spellchecking

By default CefSettings.Locale will dictate which dictionary is used, the default being en-US. It is possible to configure many aspects of spell checking enable/disable on the fly, change dictionary on the fly, even enable multiple dictionaries. Use RequestContext.SetPreference (See the RequestContext section of this document for details on how to set a preference).

Spellcheck can only be changed dynamically using spellcheck.dictionaries preference (important to use the plural version) https://github.com/chromiumembedded/cef/issues/2222#issuecomment-1465009296

Here are some useful links

http://magpcss.org/ceforum/viewtopic.php?f=6&t=14911&p=33882&hilit=spellcheck#p33882 https://cs.chromium.org/chromium/src/components/spellcheck/browser/pref_names.cc?type=cs&q=%22spellcheck.dictionary%22&l=11 https://cs.chromium.org/chromium/src/components/spellcheck/browser/pref_names.cc?type=cs&q=%22spellcheck.dictionary%22&l=15

Not all language support spell checking, see https://magpcss.org/ceforum/viewtopic.php?f=6&t=16508#p40684

WebAssembly

Is enabled by default in newer builds see https://www.chromestatus.com/feature/5453022515691520

For older versions you need to manually enable WebAssembly see https://bitbucket.org/chromiumembedded/cef/issues/2101/add-webassembly-support

settings.javascript_flags translates to settings.JavascriptFlags = "--expose-wasm";

Exception Handling

Capturing unmanaged exceptions is difficult and CEF could potentially be in a corrupted state requiring your application to terminate and restart. As this is a general programming topic and outside the scope of CefSharp specifically here are some resources to get you started researching this for yourself.

http://stackoverflow.com/questions/233255/how-does-setunhandledexceptionfilter-work-in-net-winforms-applications https://msdn.microsoft.com/en-us/library/windows/desktop/ms680634(v=vs.85).aspx https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/Application.cs,8243b844777a16c3 https://referencesource.microsoft.com/#System.Windows.Forms/winforms/Managed/System/WinForms/Application.cs,3192

Capturing unhandled exceptions in a mixed native/CLR environment http://www.ikriv.com/blog/?p=1440

Dependency Checking

CefSharp has a very simple class that checks to see if the all the relevant unmanaged resources are present.

//Perform dependency check to make sure all relevant resources are in our output directory.
//https://cefsharp.github.io/api/118.6.x/html/M_CefSharp_Cef_Initialize_1.htm
Cef.Initialize(settings, performDependencyCheck: true, browserProcessHandler: null);

//Manually check
//https://cefsharp.github.io/api/118.6.x/html/T_CefSharp_DependencyChecker.htm
DependencyChecker.AssertAllDependenciesPresent(cefSettings.Locale, cefSettings.LocalesDirPath, cefSettings.ResourcesDirPath, cefSettings.PackLoadingDisabled, cefSettings.BrowserSubprocessPath);

It's not 100% foolproof, if your having problems and all resources exist then disable dependency checking. There are certain scenarios when it's not going to work.

https://github.com/cefsharp/CefSharp/wiki/Output-files-description-table-%28Redistribution%29

Multimedia (Audio/Video)

CEF and subsequently CefSharp only supports freely available audio and video codecs. To see what the version of CefSharp you are working with supports open http://html5test.com/ in a ChromiumWebBrowser instance.

  • MP3 patent has expired and as a result is supported in version 65.0.0 on wards.
  • H264/AAC are classed as Proprietary Codecs and are not supported, they require you to obtain a license. Sites like Netflix/Twitter/Instagram use H264 and as a result their videos won't play. See https://www.fsf.org/licensing/h264-patent-license for some comments from the Free Software Foundation on the subject.

Compiling CEF with support for H264/AAC is outside the scope of this project. The following are provided for reference only, please don't ask for support for compiling CEF.

OnScreen (Virtual) Keyboard

The WinForms version has built in support for onscreen keyboard, it has been reported that on occasion it doesn't always popup correctly, using disable-usb-keyboard-detect command line argument https://github.com/cefsharp/CefSharp/issues/1691#issuecomment-323603277 has reported to resolve this problem.

The WPF does not have built in support for onscreen (virtual) keyboard, starting with version 73 a new VirtualKeyboardRequested event now provides notification when you application should display a virtual keyboard. Unfortunately it's difficult to provide a default implementation that supports Windows 7, 8.1 and 10 as there is no .Net API for display a virtual keyboard. A Windows 10 Only example was added in https://github.com/cefsharp/CefSharp/commit/0b57e526158e57e522d46671404c557256529416 If you need to support Windows 8 and 10 then https://github.com/maximcus/WPFTabTip might be useful. For Windows 7 https://stackoverflow.com/questions/1168203/incorporating-the-windows-7-onscreen-keyboard-into-a-wpf-app has some suggestions.

Protocol Execution

The following example calls Process.Start to open a mailto link with the default associated mail client.

public class CustomRequestHandler : CefSharp.Handler.RequestHandler
{
	protected override bool OnBeforeBrowse(IWebBrowser chromiumWebBrowser, IBrowser browser, IFrame frame, IRequest request, bool userGesture, bool isRedirect)
	{
		//For security reasons you should perform validation on the url to confirm that it's safe before proceeding.
		if (request.Url.StartsWith("mailto:"))
		{
			//Cancel the request and defer to Windows to open the Url with the associated
			//Handler (in this case the default email client should be opened).
			Process.Start(request.Url);
			return true;
		}
		return base.OnBeforeBrowse(chromiumWebBrowser, browser, frame, request, userGesture, isRedirect);
	}
}

browser.RequestHandler = new CustomRequestHandler();

Cookie Manager

It's possible to create/retrieve/update/delete cookies via the ICookieManager. By default all browsers share the same ICookieManager which can be accessed via Cef.GetGlobalCookieManager. The cookie managers storage is created in an async fashion, whilst this method may return a cookie manager instance, there may be a short delay before you can create/retrieve/update/delete cookies.

Create/Update Cookie

Using ICookieManager.SetCookie.

  • Using the name of an existing cookie will update it's value/expiry/etc.
  • Cookie will be created in an async fashion, see ICookieManager.SetCookieAsync below if you need to wait for the cookie to be created.
using CefSharp;

var cookieManager = Cef.GetGlobalCookieManager();

//success == false if an invalid URL is specified or if cookies cannot be accessed.
//The cookie itself will be created/updated async, use SetCookieAsync (example below) to be sure
//the cookie has been created/updated successfully.
var success = cookieManager.SetCookie("custom://cefsharp/home.html", new Cookie
{
	Name = "CefSharpTestCookie",
	Value = "ILikeCookies",
	Expires = DateTime.Now.AddDays(1)
});

Cookies are created in an async fashion, using ICookieManager.SetCookieAsync if you need to make sure the cookie has been created before continuing then use

using CefSharp;

var cookieManager = Cef.GetGlobalCookieManager();

//If success == true the cookie will have been created/updated successfully.
var success = await cookieManager.SetCookieAsync("custom://cefsharp/home.html", new Cookie
{
	Name = "CefSharpTestCookie",
	Value = "ILikeCookies",
	Expires = DateTime.Now.AddDays(1)
});

Delete Cookie(s)

Using ICookieManager.DeleteCookiesAsync or ICookieManager.DeleteCookies you can delete just a single cookie by name, all cookies for a Url or all cookies for the ICookieManager

using CefSharp;

var cookieManager = Cef.GetGlobalCookieManager();

//Delete cookies by name
await cookieManager.DeleteCookiesAsync(url: "custom://cefsharp/home.html", name: "CefSharpTestCookie");

//Delete all cookies for a Url
await cookieManager.DeleteCookiesAsync(url: "custom://cefsharp/home.html");

//Delete all cookies for the cookie manager
await cookieManager.DeleteCookiesAsync();

Retrieve Cookies

Get all cookies for a Url using ICookieManager.VisitUrlCookiesAsync

using CefSharp;

var cookieManager = Cef.GetGlobalCookieManager();

//Using await
var result = await cookieManager.VisitUrlCookiesAsync("custom://cefsharp/home.html", includeHttpOnly: false);
var cookieCount = result.Count;

//Using ContinueWith
cookieManager.VisitUrlCookiesAsync("custom://cefsharp/home.html", includeHttpOnly: false).ContinueWith(t =>
{
	if (t.Status == TaskStatus.RanToCompletion)
	{
		//All the cookies for the specified URL
		var cookies = t.Result;

		foreach (var cookie in cookies)
		{
			Debug.WriteLine("CookieName: " + cookie.Name);
		}
	}
	else
	{
		Debug.WriteLine("No Cookies found");
	}
});

If you are using multiple RequestContexts then you can use the IWebBrowser.GetCookieManager extension method. (All instances of ChromiumWebBrowser implement IWebBrowser). This will also work when using the default Global Cookie Manager.

using CefSharp;

var cookieManager = chromiumWebBrowser.GetCookieManager();
var result = await cookieManager.VisitUrlCookiesAsync("custom://cefsharp/home.html", includeHttpOnly: false);
var cookieCount = result.Count;

Cookie Manager Initialized

If you need to wait for the Cookie Store to initialize so you can set cookies before your first ChromiumWebBrowser is created there are a few options including:

using CefSharp;

public class BrowserProcessHandler : IBrowserProcessHandler
{
	void IBrowserProcessHandler.OnContextInitialized()
	{
		//The Global CookieManager has been initialized, you can now create/retrieve/update/delete cookies
		var cookieManager = Cef.GetGlobalCookieManager();

		
	}

	void IBrowserProcessHandler.OnScheduleMessagePumpWork(long delay)
	{
		
	}

	public virtual void Dispose()
	{

	}
}

var settings = new CefSettings()
{
	//By default CefSharp will use an in-memory cache, you need to specify a Cache Folder to persist data
	CachePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "CefSharp\\Cache")
};

Cef.Initialize(settings, performDependencyCheck: true, browserProcessHandler: new BrowserProcessHandler());

Alternatively Cef.GetGlobalCookieManager takes a ICompletionCallback param which can be used to wait for the cookie store to be initialized. TaskCompletionCallback is a default implement that exposes a Task.

using CefSharp;

var callback = new TaskCompletionCallback();
var cookieManager = Cef.GetGlobalCookieManager(callback);

await callback.Task.ConfigureAwait(false);

return cookieManager;

SSL/TLS Certificate Errors

Option 1 (Preferred)

Implement IRequestHandler.OnCertificateError - this method will be called for every invalid certificate. If you only wish to override a few methods of IRequestHandler then you can inherit from RequestHandler and override the methods you are interested in specifically, in this case OnCertificateError

//Make sure you assign your RequestHandler instance to the `ChromiumWebBrowser`
browser.RequestHandler = new ExampleRequestHandler();

public class ExampleRequestHandler : RequestHandler
{
    protected override bool OnCertificateError(IWebBrowser chromiumWebBrowser, IBrowser browser, CefErrorCode errorCode, string requestUrl, ISslInfo sslInfo, IRequestCallback callback)
    {
        //NOTE: I suggest wrapping callback in a using statement or explicitly execute callback.Dispose as callback wraps an unmanaged resource.

        //Example #1
        //Return true and call IRequestCallback.Continue() at a later time to continue or cancel the request.
        //In this instance we'll use a Task, typically you'd invoke a call to the UI Thread and display a Dialog to the user
        Task.Run(() =>
        {
            //NOTE: When executing the callback in an async fashion need to check to see if it's disposed
            if (!callback.IsDisposed)
            {
                using (callback)
                {
                    //We'll allow the expired certificate from badssl.com
                    if (requestUrl.ToLower().Contains("https://expired.badssl.com/"))
                    {
                        callback.Continue(true);
                    }
                    else
                    {
                        callback.Continue(false);
                    }
                }
            }
        });

        return true;

        //Example #2
        //Execute the callback and return true to immediately allow the invalid certificate
        //callback.Continue(true); //Callback will Dispose it's self once exeucted
        //return true;

        //Example #3
        //Return false for the default behaviour (cancel request immediately)
        //callback.Dispose(); //Dispose of callback
        //return false;
    }
}

Option 2

Set ignore-certificate-errors command line arg. This will ignore all certificate errors, no calls to IRequestHandler.OnCertificateError will be made.

var settings = new CefSettings();
settings.CefCommandLineArgs.Add("ignore-certificate-errors");

Cef.Initialize(settings);

Saving Downloads

To enable saving of downloaded files you need to assign an instance of IDownloadHandler to the ChromiumWebBrowser.DownloadHandler property.

The examples below will use the Fluent implementation for ease of use, you can use any of the following:

Always save to specific folder

using CefSharp.Fluent;

//Save all files to temp folder, update to whatever suites you.
var userTempPath = System.IO.Path.GetTempPath();

chromiumWebBrowser.DownloadHandler =
                    DownloadHandler.UseFolder(userTempPath,
                        (chromiumBrowser, browser, downloadItem, callback) =>
                        {
                            // To access the UI you'll need to use the Dispatcher.InvokeAsync (WPF)
                            // or Control.BeginInvoke (WinForms)
                            if(downloadItem.IsComplete)
                            {
                                //TODO: Add code here
                            }
                            else if(downloadItem.IsCancelled)
                            {
                                //TODO: Add code here
                            }
                        });

Ask user where to save files

using CefSharp.Fluent;

chromiumWebBrowser.DownloadHandler =
                    Fluent.DownloadHandler.AskUser((chromiumBrowser, browser, downloadItem, callback) =>
                        {
                            // To access the UI you'll need to use the Dispatcher.InvokeAsync (WPF)
                            // or Control.BeginInvoke (WinForms)
                            if(downloadItem.IsComplete)
                            {
                                //TODO: Add code here
                            }
                            else if(downloadItem.IsCancelled)
                            {
                                //TODO: Add code here
                            }
                        });

Save download WPF Example

A simple WPF example might look something like the following:

using CefSharp.Fluent;

browser.DownloadHandler = CefSharp.Fluent.DownloadHandler
	.Create()
	.CanDownload((chromiumWebBrowser, browser, url, requestMethod) =>
	{
		//All all downloads
		return true;
	})
	.OnBeforeDownload((chromiumWebBrowser, browser, downloadItem, callback) =>
	{
		UpdateDownloadAction("OnBeforeDownload", downloadItem);

		callback.Continue("", showDialog: true);

	}).OnDownloadUpdated((chromiumWebBrowser, browser, downloadItem, callback) =>
	{
		UpdateDownloadAction("OnDownloadUpdated", downloadItem);
	})
	.Build();
	
private void UpdateDownloadAction(string downloadAction, DownloadItem downloadItem)
{
  // Invoke on the WPF UI Thread
	this.Dispatcher.InvokeAsync(() =>
	{
		var viewModel = (BrowserTabViewModel)this.DataContext;
		viewModel.LastDownloadAction = downloadAction;
		viewModel.DownloadItem = downloadItem;
	});
}

Hide popup window opened by download

For downloads that open a popup window it maybe desirable to hide that popup once the download has started, closing once complete or cancelled.

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool IsWindowVisible(IntPtr hWnd);

[DllImport("user32.dll")]
private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

var tempPath = System.IO.Path.GetTempPath();

browser.DownloadHandler =
	Fluent.DownloadHandler.UseFolder(tempPath,
		(chromiumBrowser, browser, downloadItem, callback) =>
		{
      // To access the UI you'll need to use the Dispatcher.InvokeAsync (WPF)
      // or Control.BeginInvoke (WinForms)
			if (downloadItem.IsComplete || downloadItem.IsCancelled)
			{
				if (browser.IsPopup && !browser.HasDocument)
				{
					browser.GetHost().CloseBrowser(true);
				}
			}
			//TODO: You may wish to customise this condition to better suite your
			//requirements. 
			else if(downloadItem.ReceivedBytes < 100)
			{
				var popupHwnd = browser.GetHost().GetWindowHandle();

				var visible = IsWindowVisible(popupHwnd);
				if(visible)
				{
					const int SW_HIDE = 0;
					ShowWindow(popupHwnd, SW_HIDE);
				}
			}
		});

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