winui3-migration-guide

Complete reference for migrating UWP apps to WinUI 3 with before/after code examples. Use this skill when migrating UWP apps to WinUI 3 / Windows App SDK, or when verifying that generated code uses correct WinUI 3 APIs instead of legacy UWP patterns. All Windows.UI.Xaml.* namespaces move to Microsoft.UI.Xaml.* : Key difference : UWP uses ASTA (Application STA) with built-in reentrancy blocking. WinUI 3 uses standard STA without this protection. Watch for reentrancy issues when async code pumps messages. All GetForCurrentView() patterns are unavailable in WinUI 3 desktop apps: UWP unit test projects do not work with WinUI 3. You must migrate to the WinUI 3 test project templates. Key: The [UITestMethod] attribute tells the test runner to execute the test on the XAML UI thread, which is required for instantiating any Microsoft.UI.Xaml type.