API to enumerate all images contained in card

[andrewleader]

Implementation status

• JavaScript ([JS] API to enumerate all images contained in a card #1660)
• 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

Scenario

Toast notifications need to pre-load HTTP images in non-UI threads, so before any calls to Render (and any XAML tree creation) occurs.

Proposed solution

Provide an API to enumerate all images contained in a card. It's not realistic for card authors like toasts to enumerate through body/action elements themselves, since images could be contained inside columns or even inside ShowCards. This enumeration would have to be maintained and owned by Adaptive Cards.

Uri[] images = card.GetAllImageUris();

API returns all image URIs, like https://msn.com/img.png, ms-appx:///Assets/taco.png, etc... Action Center can then filter themselves whether it's a remote web image or not.

Pulls from...

• Body image elements
• Image elements contained within Container
• Image elements contained within Column
• Image elements contained within ShowCard
• Image urls contained within Action (once Action is updated to support images)
• Background image
• Anything else I'm missing

I'm not picky on the API name or the return type.

[andrewleader]

Changing priority to Tag-Toasts-V1 since it turns out this is required for Action Center to support ms-appx/ms-appdata images too, not just http, so it's something critical for RS5

[paulcam206]

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