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Winui3 Migration Guide

github/awesome-copilot
25.1k
github

This skill guides developers in migrating UWP applications to WinUI 3 and the Windows App SDK, covering namespace changes, API replacements, and window management adjustments. It highlights key differences in threading, dialogs, pickers, background tasks, and app settings, providing practical code examples for adapting legacy patterns. Designed for developers transitioning existing UWP apps to modern desktop frameworks, it ensures compatibility and smooth migration.

npx skills add https://github.com/github/awesome-copilot --skill winui3-migration-guide

WinUI 3 Migration Guide

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.

Namespace Changes

All Windows.UI.Xaml.* namespaces move to Microsoft.UI.Xaml.*: UWP Namespace WinUI 3 Namespace Windows.UI.Xaml Microsoft.UI.Xaml Windows.UI.Xaml.Controls Microsoft.UI.Xaml.Controls Windows.UI.Xaml.Media Microsoft.UI.Xaml.Media Windows.UI.Xaml.Input Microsoft.UI.Xaml.Input Windows.UI.Xaml.Data Microsoft.UI.Xaml.Data Windows.UI.Xaml.Navigation Microsoft.UI.Xaml.Navigation Windows.UI.Xaml.Shapes Microsoft.UI.Xaml.Shapes Windows.UI.Composition Microsoft.UI.Composition Windows.UI.Input Microsoft.UI.Input Windows.UI.Colors Microsoft.UI.Colors Windows.UI.Text Microsoft.UI.Text Windows.UI.Core Microsoft.UI.Dispatching (for dispatcher)

Top 3 Most Common Copilot Mistakes

1. ContentDialog Without XamlRoot

// ❌ WRONG — Throws InvalidOperationException in WinUI 3
var dialog = new ContentDialog
{
    Title = "Error",
    Content = "Something went wrong.",
    CloseButtonText = "OK"
};
await dialog.ShowAsync();

// ✅ CORRECT — Set XamlRoot before showing
var dialog = new ContentDialog
{
    Title = "Error",
    Content = "Something went wrong.",
    CloseButtonText = "OK",
    XamlRoot = this.Content.XamlRoot  // Required in WinUI 3
};
await dialog.ShowAsync();

2. MessageDialog Instead of ContentDialog

// ❌ WRONG — UWP API, not available in WinUI 3 desktop
var dialog = new Windows.UI.Popups.MessageDialog("Are you sure?", "Confirm");
await dialog.ShowAsync();

// ✅ CORRECT — Use ContentDialog
var dialog = new ContentDialog
{
    Title = "Confirm",
    Content = "Are you sure?",
    PrimaryButtonText = "Yes",
    CloseButtonText = "No",
    XamlRoot = this.Content.XamlRoot
};
var result = await dialog.ShowAsync();
if (result == ContentDialogResult.Primary)
{
    // User confirmed
}

3. CoreDispatcher Instead of DispatcherQueue

// ❌ WRONG — CoreDispatcher does not exist in WinUI 3
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
    StatusText.Text = "Done";
});

// ✅ CORRECT — Use DispatcherQueue
DispatcherQueue.TryEnqueue(() =>
{
    StatusText.Text = "Done";
});
// With priority:
DispatcherQueue.TryEnqueue(DispatcherQueuePriority.High, () =>
{
    ProgressBar.Value = 100;
});

Windowing Migration

Window Reference

// ❌ WRONG — Window.Current does not exist in WinUI 3
var currentWindow = Window.Current;

// ✅ CORRECT — Use a static property in App
public partial class App : Application
{
    public static Window MainWindow { get; private set; }
    protected override void OnLaunched(LaunchActivatedEventArgs args)
    {
        MainWindow = new MainWindow();
        MainWindow.Activate();
    }
}
// Access anywhere: App.MainWindow

Window Management

UWP API WinUI 3 API ApplicationView.TryResizeView() AppWindow.Resize() AppWindow.TryCreateAsync() AppWindow.Create() AppWindow.TryShowAsync() AppWindow.Show() AppWindow.TryConsolidateAsync() AppWindow.Destroy() AppWindow.RequestMoveXxx() AppWindow.Move() AppWindow.GetPlacement() AppWindow.Position property AppWindow.RequestPresentation() AppWindow.SetPresenter()

Title Bar

UWP API WinUI 3 API CoreApplicationViewTitleBar AppWindowTitleBar CoreApplicationView.TitleBar.ExtendViewIntoTitleBar AppWindow.TitleBar.ExtendsContentIntoTitleBar

Dialogs and Pickers Migration

File/Folder Pickers

// ❌ WRONG — UWP style, no window handle
var picker = new FileOpenPicker();
picker.FileTypeFilter.Add(".txt");
var file = await picker.PickSingleFileAsync();

// ✅ CORRECT — Initialize with window handle
var picker = new FileOpenPicker();
var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(App.MainWindow);
WinRT.Interop.InitializeWithWindow.Initialize(picker, hwnd);
picker.FileTypeFilter.Add(".txt");
var file = await picker.PickSingleFileAsync();

Threading Migration

UWP Pattern WinUI 3 Equivalent CoreDispatcher.RunAsync(priority, callback) DispatcherQueue.TryEnqueue(priority, callback) Dispatcher.HasThreadAccess DispatcherQueue.HasThreadAccess CoreDispatcher.ProcessEvents() No equivalent — restructure async code CoreWindow.GetForCurrentThread() Not available — use DispatcherQueue.GetForCurrentThread() 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.

Background Tasks Migration

// ❌ WRONG — UWP IBackgroundTask
public sealed class MyTask : IBackgroundTask
{
    public void Run(IBackgroundTaskInstance taskInstance) { }
}

// ✅ CORRECT — Windows App SDK AppLifecycle
using Microsoft.Windows.AppLifecycle;
// Register for activation
var args = AppInstance.GetCurrent().GetActivatedEventArgs();
if (args.Kind == ExtendedActivationKind.AppNotification)
{
    // Handle background activation
}

App Settings Migration

Scenario Packaged App Unpackaged App Simple settings ApplicationData.Current.LocalSettings JSON file in LocalApplicationData Local file storage ApplicationData.Current.LocalFolder Environment.GetFolderPath(SpecialFolder.LocalApplicationData)

GetForCurrentView() Replacements

All GetForCurrentView() patterns are unavailable in WinUI 3 desktop apps: UWP API WinUI 3 Replacement UIViewSettings.GetForCurrentView() Use AppWindow properties ApplicationView.GetForCurrentView() AppWindow.GetFromWindowId(windowId) DisplayInformation.GetForCurrentView() Win32 GetDpiForWindow() or XamlRoot.RasterizationScale CoreApplication.GetCurrentView() Not available — track windows manually SystemNavigationManager.GetForCurrentView() Handle back navigation in NavigationView directly

Testing Migration

UWP unit test projects do not work with WinUI 3. You must migrate to the WinUI 3 test project templates. UWP WinUI 3 Unit Test App (Universal Windows) Unit Test App (WinUI in Desktop) Standard MSTest project with UWP types Must use WinUI test app for Xaml runtime [TestMethod] for all tests [TestMethod] for logic, [UITestMethod] for XAML/UI tests Class Library (Universal Windows) Class Library (WinUI in Desktop)

// ✅ WinUI 3 unit test — use [UITestMethod] for any XAML interaction
[UITestMethod]
public void TestMyControl()
{
    var control = new MyLibrary.MyUserControl();
    Assert.AreEqual(expected, control.MyProperty);
}

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.

Migration Checklist

  1. Replace all Windows.UI.Xaml.* using directives with Microsoft.UI.Xaml.*
  2. Replace Windows.UI.Colors with Microsoft.UI.Colors
  3. Replace CoreDispatcher.RunAsync with DispatcherQueue.TryEnqueue
  4. Replace Window.Current with App.MainWindow static property
  5. Add XamlRoot to all ContentDialog instances
  6. Initialize all pickers with InitializeWithWindow.Initialize(picker, hwnd)
  7. Replace MessageDialog with ContentDialog
  8. Replace ApplicationView/CoreWindow with AppWindow
  9. Replace CoreApplicationViewTitleBar with AppWindowTitleBar
  10. Replace all GetForCurrentView() calls with AppWindow equivalents
  11. Update interop for Share and Print managers
  12. Replace IBackgroundTask with AppLifecycle activation
  13. Update project file: TFM to net10.0-windows10.0.22621.0, add <UseWinUI>true</UseWinUI>
  14. Migrate unit tests to Unit Test App (WinUI in Desktop) project; use [UITestMethod] for XAML tests
  15. Test both packaged and unpackaged configurations

GitHub Owner

Owner: github

GitHub Links

SKILL.md

name: winui3-migration-guide description: 'UWP-to-WinUI 3 migration reference. Maps legacy UWP APIs to correct Windows App SDK equivalents with before/after code snippets. Covers namespace changes, threading (CoreDispatcher to DispatcherQueue), windowing (CoreWindow to AppWindow), dialogs, pickers, sharing, printing, background tasks, and the most common Copilot code generation mistakes.'

WinUI 3 Migration Guide

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.

Namespace Changes

All Windows.UI.Xaml.* namespaces move to Microsoft.UI.Xaml.*:

UWP NamespaceWinUI 3 Namespace
Windows.UI.XamlMicrosoft.UI.Xaml
Windows.UI.Xaml.ControlsMicrosoft.UI.Xaml.Controls
Windows.UI.Xaml.MediaMicrosoft.UI.Xaml.Media
Windows.UI.Xaml.InputMicrosoft.UI.Xaml.Input
Windows.UI.Xaml.DataMicrosoft.UI.Xaml.Data
Windows.UI.Xaml.NavigationMicrosoft.UI.Xaml.Navigation
Windows.UI.Xaml.ShapesMicrosoft.UI.Xaml.Shapes
Windows.UI.CompositionMicrosoft.UI.Composition
Windows.UI.InputMicrosoft.UI.Input
Windows.UI.ColorsMicrosoft.UI.Colors
Windows.UI.TextMicrosoft.UI.Text
Windows.UI.CoreMicrosoft.UI.Dispatching (for dispatcher)

Top 3 Most Common Copilot Mistakes

1. ContentDialog Without XamlRoot

// ❌ WRONG — Throws InvalidOperationException in WinUI 3
var dialog = new ContentDialog
{
    Title = "Error",
    Content = "Something went wrong.",
    CloseButtonText = "OK"
};
await dialog.ShowAsync();

// ✅ CORRECT — Set XamlRoot before showing
var dialog = new ContentDialog
{
    Title = "Error",
    Content = "Something went wrong.",
    CloseButtonText = "OK",
    XamlRoot = this.Content.XamlRoot  // Required in WinUI 3
};
await dialog.ShowAsync();

2. MessageDialog Instead of ContentDialog

// ❌ WRONG — UWP API, not available in WinUI 3 desktop
var dialog = new Windows.UI.Popups.MessageDialog("Are you sure?", "Confirm");
await dialog.ShowAsync();

// ✅ CORRECT — Use ContentDialog
var dialog = new ContentDialog
{
    Title = "Confirm",
    Content = "Are you sure?",
    PrimaryButtonText = "Yes",
    CloseButtonText = "No",
    XamlRoot = this.Content.XamlRoot
};
var result = await dialog.ShowAsync();
if (result == ContentDialogResult.Primary)
{
    // User confirmed
}

3. CoreDispatcher Instead of DispatcherQueue

// ❌ WRONG — CoreDispatcher does not exist in WinUI 3
await Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>
{
    StatusText.Text = "Done";
});

// ✅ CORRECT — Use DispatcherQueue
DispatcherQueue.TryEnqueue(() =>
{
    StatusText.Text = "Done";
});
// With priority:
DispatcherQueue.TryEnqueue(DispatcherQueuePriority.High, () =>
{
    ProgressBar.Value = 100;
});

Windowing Migration

Window Reference

// ❌ WRONG — Window.Current does not exist in WinUI 3
var currentWindow = Window.Current;

// ✅ CORRECT — Use a static property in App
public partial class App : Application
{
    public static Window MainWindow { get; private set; }
    protected override void OnLaunched(LaunchActivatedEventArgs args)
    {
        MainWindow = new MainWindow();
        MainWindow.Activate();
    }
}
// Access anywhere: App.MainWindow

Window Management

UWP APIWinUI 3 API
ApplicationView.TryResizeView()AppWindow.Resize()
AppWindow.TryCreateAsync()AppWindow.Create()
AppWindow.TryShowAsync()AppWindow.Show()
AppWindow.TryConsolidateAsync()AppWindow.Destroy()
AppWindow.RequestMoveXxx()AppWindow.Move()
AppWindow.GetPlacement()AppWindow.Position property
AppWindow.RequestPresentation()AppWindow.SetPresenter()

Title Bar

UWP APIWinUI 3 API
CoreApplicationViewTitleBarAppWindowTitleBar
CoreApplicationView.TitleBar.ExtendViewIntoTitleBarAppWindow.TitleBar.ExtendsContentIntoTitleBar

Dialogs and Pickers Migration

File/Folder Pickers

// ❌ WRONG — UWP style, no window handle
var picker = new FileOpenPicker();
picker.FileTypeFilter.Add(".txt");
var file = await picker.PickSingleFileAsync();

// ✅ CORRECT — Initialize with window handle
var picker = new FileOpenPicker();
var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(App.MainWindow);
WinRT.Interop.InitializeWithWindow.Initialize(picker, hwnd);
picker.FileTypeFilter.Add(".txt");
var file = await picker.PickSingleFileAsync();

Threading Migration

UWP PatternWinUI 3 Equivalent
CoreDispatcher.RunAsync(priority, callback)DispatcherQueue.TryEnqueue(priority, callback)
Dispatcher.HasThreadAccessDispatcherQueue.HasThreadAccess
CoreDispatcher.ProcessEvents()No equivalent — restructure async code
CoreWindow.GetForCurrentThread()Not available — use DispatcherQueue.GetForCurrentThread()
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.

Background Tasks Migration

// ❌ WRONG — UWP IBackgroundTask
public sealed class MyTask : IBackgroundTask
{
    public void Run(IBackgroundTaskInstance taskInstance) { }
}

// ✅ CORRECT — Windows App SDK AppLifecycle
using Microsoft.Windows.AppLifecycle;
// Register for activation
var args = AppInstance.GetCurrent().GetActivatedEventArgs();
if (args.Kind == ExtendedActivationKind.AppNotification)
{
    // Handle background activation
}

App Settings Migration

ScenarioPackaged AppUnpackaged App
Simple settingsApplicationData.Current.LocalSettingsJSON file in LocalApplicationData
Local file storageApplicationData.Current.LocalFolderEnvironment.GetFolderPath(SpecialFolder.LocalApplicationData)

GetForCurrentView() Replacements

All GetForCurrentView() patterns are unavailable in WinUI 3 desktop apps:

UWP APIWinUI 3 Replacement
UIViewSettings.GetForCurrentView()Use AppWindow properties
ApplicationView.GetForCurrentView()AppWindow.GetFromWindowId(windowId)
DisplayInformation.GetForCurrentView()Win32 GetDpiForWindow() or XamlRoot.RasterizationScale
CoreApplication.GetCurrentView()Not available — track windows manually
SystemNavigationManager.GetForCurrentView()Handle back navigation in NavigationView directly

Testing Migration

UWP unit test projects do not work with WinUI 3. You must migrate to the WinUI 3 test project templates.

UWPWinUI 3
Unit Test App (Universal Windows)Unit Test App (WinUI in Desktop)
Standard MSTest project with UWP typesMust use WinUI test app for Xaml runtime
[TestMethod] for all tests[TestMethod] for logic, [UITestMethod] for XAML/UI tests
Class Library (Universal Windows)Class Library (WinUI in Desktop)
// ✅ WinUI 3 unit test — use [UITestMethod] for any XAML interaction
[UITestMethod]
public void TestMyControl()
{
    var control = new MyLibrary.MyUserControl();
    Assert.AreEqual(expected, control.MyProperty);
}

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.

Migration Checklist

  1. Replace all Windows.UI.Xaml.* using directives with Microsoft.UI.Xaml.*
  2. Replace Windows.UI.Colors with Microsoft.UI.Colors
  3. Replace CoreDispatcher.RunAsync with DispatcherQueue.TryEnqueue
  4. Replace Window.Current with App.MainWindow static property
  5. Add XamlRoot to all ContentDialog instances
  6. Initialize all pickers with InitializeWithWindow.Initialize(picker, hwnd)
  7. Replace MessageDialog with ContentDialog
  8. Replace ApplicationView/CoreWindow with AppWindow
  9. Replace CoreApplicationViewTitleBar with AppWindowTitleBar
  10. Replace all GetForCurrentView() calls with AppWindow equivalents
  11. Update interop for Share and Print managers
  12. Replace IBackgroundTask with AppLifecycle activation
  13. Update project file: TFM to net10.0-windows10.0.22621.0, add <UseWinUI>true</UseWinUI>
  14. Migrate unit tests to Unit Test App (WinUI in Desktop) project; use [UITestMethod] for XAML tests
  15. Test both packaged and unpackaged configurations

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