WebView widget does not load with Windows Store Python

[Jzhenli]

Describe the bug

Hi, I have try webview widget on win11, and it not works.

Steps to reproduce

the test code as below:

class testweb(toga.App):
    def startup(self):
        self.main_window = toga.MainWindow()

        self.webview = toga.WebView(
            on_webview_load=self.on_webview_loaded, style=Pack(flex=1)
        )
        self.url_input = toga.TextInput(
            value="https://beeware.org/", style=Pack(flex=1)
        )

        box = toga.Box(
            children=[
                toga.Box(
                    children=[
                        self.url_input,
                        toga.Button(
                            "Go",
                            on_press=self.load_page,
                            style=Pack(width=50, padding_left=5),
                        ),
                    ],
                    style=Pack(
                        direction=ROW,
                        alignment=CENTER,
                        padding=5,
                    ),
                ),
                self.webview,
            ],
            style=Pack(direction=COLUMN),
        )

        self.main_window.content = box
        self.webview.url = self.url_input.value

        # Show the main window
        self.main_window.show()

    def load_page(self, widget):
        self.webview.url = self.url_input.value

    def on_webview_loaded(self, widget):
        self.url_input.value = self.webview.url

Expected behavior

webview not display as below image:

Expected: the webview should display

Screenshots

No response

Environment

• Operating System: win11 home edition 23H2
• Python version: Python 3.10.11
• Software versions:
  • Briefcase: 0.3.19
  • Toga:0.4.5

Logs

Additional context

No response

[freakboy3742]

Thanks for the report; unfortunately, I can't reproduce this problem.

If you're not receiving any other errors about the availability of the Edge webview, then my best guess is that the underlying problem is a timing error in this specific example.

If you click the "go" button, does it load the webpage? If so, then the issue could be that the webview is working, but the order of page loads is getting confused. The webview is originally being created with no initial URL; and that (empty) page is loading successfully, but because there's a load in progress, the subsequent URL change is being lost.

[Jzhenli]

@freakboy3742 I add a print message in the load_page function, when click the "go" button, it will print, but no webview display.

[freakboy3742]

This suggests the issue might be layout.

If you add a widget (say, a toga.Label) to the column box after the web view - does that widget appear in the GUI directly under the text input and button? If so, the webview is there, it's just being rendered as zero height, and therefore invisible - although I'm not sure why that would be happening.

[Jzhenli]

@freakboy3742 I add a test label, and repeat to click the button, but the webview widget still doesn't appear in the GUI.

[freakboy3742]

To confirm - your console log isn't showing anything errors or warnings about the web view when the app starts?

[Jzhenli]

yes, no error in the console log @freakboy3742

[freakboy3742]

I'm at a loss - I can't work out what is going on here.

The WebView2 assembly must be successfully loading, or you'd be getting errors in the console. I can only assume that the control isn't initialising - and isn't failing to initialise either, because if it was failing you'd be getting an error. You might be able to clarify this by putting some additional logging into Toga's winforms backend, on the WebView.winforms_initialization_completed method - this should be invoked, but the behavior you're seeing suggests it isn't.

I've done a quick search and there's some suggestions this might be related to the .NET runtime version that you have installed - what version have you got?

[Jzhenli]

@freakboy3742 I haven't install any .NET runtime before, and now I try install the dotnet-sdk-8.0.303-win-x64, but the webview widget still not works.

[freakboy3742]

I'm afraid I'm at a complete loss. As I can't reproduce your problem, it's very hard for me to investigate further. All I can suggest is that you trace through the code and try and identify what is (and isn't) happening during startup - such as tracking whether the WebView.winforms_initialization_completed method is being invoked, as I mentioned earlier. If you're able to find the source of the problem - or even a hint about where the source of the problem might lie - then we're happy to address the problem, but until we know what the problem is, there's not much we can do.

[Jzhenli]

@freakboy3742 I have add log in the WebView.winforms_initialization_completed, it print out RuntimeError :can not find the WebView2Loader.dll

[rmartin16]

@Jzhenli: The "file not found" problem triggered a thought; are you using Python from the Windows Store?

I was able to successfully recreate this behavior using the Windows Store Python:

[helloworld] Starting in dev mode...
===========================================================================
args.InitializationException=DllNotFoundException('Unable to load DLL 'WebView2Loader.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)')

@freakboy3742, does winforms_initialization_completed() run in another thread? Trying to understand where this RuntimeError is going...

[Jzhenli]

@rmartin16 yes, I used the python from the Windows Store.

[rmartin16]

@rmartin16 yes, I used the python from the Windows Store.

Thank you for the confirmation. I don't know the exact mechanism yet but Windows Store Python can do strange things with passing file paths outside of Python.

@freakboy3742, does winforms_initialization_completed() run in another thread? Trying to understand where this RuntimeError is going...

I confirmed it's the same thread. Moreover, it looks like Exceptions raised in this callback are just completely swallowed by .NET; I even tried calling sys.exit(1) and even that was swallowed. Looks like another approach will be necessary here. The MapView is similarly affected.

[rmartin16]

@Jzhenli, I believe I tracked this down today; if you'd like to try out my proposed fix, you can update your pyproject.toml similar to below and run briefcase dev -r:

[tool.briefcase.app.helloworld.windows]
requires = [
    #"toga-winforms~=0.4.5",
    'git+https://github.com/rmartin16/toga@webview-for-winstore-python#subdirectory=core',
    'git+https://github.com/rmartin16/toga@webview-for-winstore-python#subdirectory=winforms',
]

[Jzhenli]

@rmartin16 I have download the WebView2Loader.dll and register it to the windows os, now it works well. I'm not sure if your solution have fix it, because I can't reproduce this problem, but I have tried as your suggestion, and it seems works.