Reintroduce XAML Island Helpers

[myth384]

Describe the bug

Like was written on the 8.0 release notes, Windows App SDK 1.4 indeed introduced XAML Island support, but only by adding DesktopWindowXamlSource. The Hosting API of WinUI 3 looks comparable to UWP. There are no convenience wrappers available around this class, like the WindowsXamlHost control from Microsoft.Toolkit.Win32. The absence of such control makes XAML Islands impractical for migrating WPF/WinForms apps to WinUI 3. Therefore I want to suggest to reconsider implementing WindowsXamlHost.

Steps to reproduce

Not applicable.

Expected behavior

Not applicable.

Screenshots

No response

Code Platform

• [ ] UWP
• [X] WinAppSDK / WinUI 3
• [ ] Web Assembly (WASM)
• [ ] Android
• [ ] iOS
• [ ] MacOS
• [ ] Linux / GTK

Windows Build Number

• [ ] Windows 10 1809 (Build 17763)
• [ ] Windows 10 1903 (Build 18362)
• [ ] Windows 10 1909 (Build 18363)
• [ ] Windows 10 2004 (Build 19041)
• [ ] Windows 10 20H2 (Build 19042)
• [ ] Windows 10 21H1 (Build 19043)
• [ ] Windows 10 21H2 (Build 19044)
• [ ] Windows 10 22H2 (Build 19045)
• [ ] Windows 11 21H2 (Build 22000)
• [ ] Other (specify)

Other Windows Build number

No response

App minimum and target SDK version

• [ ] Windows 10, version 1809 (Build 17763)
• [ ] Windows 10, version 1903 (Build 18362)
• [ ] Windows 10, version 1909 (Build 18363)
• [ ] Windows 10, version 2004 (Build 19041)
• [ ] Windows 10, version 2104 (Build 20348)
• [ ] Windows 11, version 22H2 (Build 22000)
• [ ] Other (specify)

Other SDK version

No response

Visual Studio Version

No response

Visual Studio Build Number

No response

Device form factor

No response

Additional context

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Help us help you

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[michael-hawker]

@myth384 originally these wrappers shipped in the Toolkit as WinUI didn't exist as a library yet originally.

If there aren't sufficient helpers with what's shipped in the WindowsAppSDK/WinUI, then we should file an issue there for them to ship alongside the APIs that support these scenarios vs. living in the Toolkit.

Would you mind refiling this on the WinUI repo? I can't transfer this here.

Feel free to call out this and other related issues/discussions on this topic:

• Reintroduce XAML Island Helpers · Issue #338 · CommunityToolkit/Windows (github.com)
• How to use Xaml Islands in a .NET WPF App? · microsoft/WindowsAppSDK · Discussion #3940 (github.com)
• Place WinUI 3 controll in XAML of WPF (.NET 6) · microsoft/WindowsAppSDK · Discussion #3778 (github.com)
• How to open a WinUI Window from a WinForms project · microsoft/WindowsAppSDK · Discussion #4203 (github.com)
• Can I use WindowsAppSDK in Winforms? · microsoft/WindowsAppSDK · Discussion #2404 (github.com)