Proposal: Set owner for Microsoft.UI.Xaml.Window

[whiskhub]

Summary

Allow to set an owner window for a Microsoft.UI.Xaml.Window by providing an owner WindowId, analog to AppWindow.Create() functionality.

Rationale

• Allows to create modal/dialog windows in WinUI 3
• Ensures feature parity with traditional Win32 window and AppWindow behavior
• Ensures feature parity with other UI frameworks like WPF
• Avoid use of the discouraged SetWindowLongPtr(GWL_HWNDPARENT) API

Scope

Capability	Priority
Allow to set owner window for Microsoft.UI.Xaml.Window during construction	Must

Important Notes

Example API

public Window();
public Window(WindowId ownerWindowId);

Also see microsoft/WindowsAppSDK#3680.

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