Add OnDevice Markup Extension

[michael-hawker]

I'm submitting a...

Once Uno supports Markup Extension with unoplatform/uno#39, it'd be cool if the OnDevice one could support other platforms as well from Uno. 😊 (Android, iOS, WASM)

• Feature request

Current behavior

https://github.com/windows-toolkit/WindowsCommunityToolkit/blob/master/Microsoft.Toolkit.Uwp.UI/Extensions/Markup/OnDevice.cs

unoplatform/uno#39

[Massimo37]

Unfortunately this still won't work in Uno due to the fact that when I process a custom MarkupExtension, I expect a MarkupExtensionReturnType to be specified. I would need to discuss this with @davidjohnoliver

[michael-hawker]

@Massimo37 could we just put a MarkupExtensionReturnType(typeof(object)) on there?

[Massimo37]

@michael-hawker yes I thought about that, it's an option I'd like to try once the PR goes through. It would be versatile if the MarkupExtensionReturnType is optional and allows a dev to return different entities (as is allowed with OnDevice).

[Massimo37]

MarkupExtensionReturnType is now optional, so that part is done. Unfortunately we still need this feature to be completed until this markup extension is usable:

unoplatform/uno#1468

[MartinZikmund]

I'm on it :-)

[MartinZikmund]

unoplatform/uno#1970