Support for UWP and System XAML

[asklar]

Filing this here to track a dependency on cswinrt from microsoft/react-native-windows#6539
We would like to be able to move away from C# UWP but we still need to target system xaml. So we would like the ability for cswinrt to target UWP apps and system XAML so that we can avoid a whole bunch of issues related to .net native and consuming nugets from C++ apps.

Related: microsoft/react-native-windows#6539

[AdamBraden]

This would require custom type mapping for xaml to map onto inbox System XAML. Right now the custom type mappings go against WinUI.

[yoshiask]

I'm a little surprised that C#/WinRT doesn't already support system XAML. Just a noob here, but I had assumed that "lifting this projection support out of the compiler and runtime" would also entail decoupling from WinUI. Are there technical reasons why it can't/won't be done?

[driver1998]

Also this will unblock the XAML islands on .NET 5+ scenario, without this we'll have to wait for WinUI 3 XAML islands which is "scheduled to a later release".

[jaigak]

I have a component that exposes a few platform XAML types. Before I could just use them from C# but now with C#/WinRT, it blacklists all those types from the projection, unlike every other WinRT projection. Even if you reserve certain mappings to Microsoft.UI.Xaml (eg: INotifyPropertyChanged), Windows.UI.Xaml types must be available even if you have Microsoft.UI.Xaml (from WinUI 3) referenced. C#/WinRT shouldn't be framework dependent. If you don't want people from using types from Windows.UI.Xaml, you should add a deprecated attribute (at least in the C#/WinRT projection), instead of not projecting them entirely.

@angelazhangmsft This issue is hanging on thin air and should be dropped right away.

UWP/CoreWindow was doomed to oblivion a loooong time ago.
As .NET 5 / .NET 6 / .NET 7 and upwards versions themselves will never support it , CsWinRT can't do very much, can it ?

[driver1998]

.NET 5 / 6 / 7 won't be compatible with AppContainer and UAP-only environments anytime soon, so UWP is not actually relevant here.
This is mainly for XAML islands.

so the title be modified to reflect XAML Island only. (Support for UWP and System XAML for XAML Islands.

<RE> well contrary to MS marketing, AppContainer is not tied to any Window specific tech (CoreWindow aka UWP)</RE>

[dongle-the-gadget]

I don't think that it is necessary, you can actually create UWP apps with .NET 6, however the incompatibility with System XAML in stock C#/WinRT blocks that.

(see https://github.com/gus33000/CsUWP)

[driver1998]

That sounds like great news, I am always baffled by the lack of XAML islands support in .NET 5/6.

[driver1998]

For those are interested, @gus33000's fork of CsWinRT is at https://github.com/gus33000/CsWinRT/tree/wux.