Support relative URLs for images in renderers

[andrewleader]

Implementation status

• JavaScript (N/A)
• UWP ([UWP] Implement API to enumerate all images in a card #1322)
• .NET ([.NET] API to enumerate all images contained in a card #1661)
• iOS ([iOS] API to enumerate all images contained in a card #1659)
• Android ([Android] API to enumerate all images contained in a card #1658)
• Documentation

Today, using a relative URL in an Adaptive Card throws an exception while rendering.

In toasts, it makes sense for us to allow relative URLs to default to ms-appx:///, which is what other XAML surfaces allow, and what existing XML toasts allow. For example, "url": "Assets/Images/dog.jpg" rather than having to write "url": "ms-appx:///Assets/Images/dog.jpg"

{
  "type": "AdaptiveCard",
  "version": "1.0",

  "title": {
    "text": "Dogs are the best!"
  },

  "body": [

    {
      "type": "Image",
      "url": "Assets/Images/dog.jpg",
      "size": "stretch"
    }

  ]
}

This requires a few pieces of work...

1. Host config where host can optionally specify a base url
2. Object model code updated to support relative URLs
3. Renderer code updated to support relative URLs and if relative, prefix the base url

1. Updated host config

{
  "supportsInteractivity": true,
  "imageBaseUrl": "ms-appx:///"
  ...

2. Object model code updated

This line of code needs to be updated to allow relative urls

BEFORE

RETURN_IF_FAILED(uriActivationFactory->CreateUri(imageUri, m_url.GetAddressOf()));

AFTER (idk what the equivalent in C++ is, but this needs to parse a URL that's either relative or absolute, allowing a relative url to be assigned)

imageUri = new Uri(imageUri, UriKind.RelativeOrAbsolute);

3. Renderer code updated

And then while rendering, this line of code needs to be updated to prefix the base url if the url is a relative url.

BEFORE

THROW_IF_FAILED(imageUri->get_SchemeName(&schemeName));

This will throw on relative urls, since relative urls don't have a scheme. Therefore, this should be updated to...

AFTER (written in C#)

// If not an absolute uri
if (!imageUri.IsAbsoluteUri)
{
    // Prefix the host config specified base url
    // Note that hostConfig.BaseUrl is a Uri object too
    imageUri = new Uri(hostConfig.BaseUrl, imageUri);
}

// Then continue with original code of getting scheme name
schemeName = imageUri.SchemeName;

[matthidinger]

Closing as not applicable to platform

[matthidinger]

Whoops, docs :)

[paulcam206]

Documentation is done and in the mahiding/site1.1 branch.