WinUI 3 and Windows App SDK

Trigger On

• building native modern Windows desktop UI on WinUI 3
• integrating Windows App SDK features into a .NET app
• deciding between WinUI, WPF, WinForms, and MAUI for Windows work
• implementing MVVM patterns in Windows App SDK applications

Workflow

1. Confirm WinUI is the right choice — use when modern Windows-native UI, Fluent Design, and Windows App SDK capabilities are needed. For cross-platform, consider MAUI instead.
2. Choose packaging model early — packaged (MSIX) vs unpackaged differ materially for deployment, identity, and API access:

``xml <!-- Unpackaged: add to .csproj --> <WindowsPackageType>None</WindowsPackageType> ``

1. Apply MVVM pattern with the MVVM Toolkit — keep views dumb, logic in ViewModels:

```csharp public partial class ProductsViewModel : ObservableObject { [ObservableProperty] private ObservableCollection<Product> _products = [];

[ObservableProperty] [NotifyCanExecuteChangedFor(nameof(DeleteCommand))] private Product? _selectedProduct;

[RelayCommand(CanExecute = nameof(CanDelete))] private async Task DeleteAsync() { if (SelectedProduct is null) return; await _productService.DeleteAsync(SelectedProduct.Id); Products.Remove(SelectedProduct); } private bool CanDelete() => SelectedProduct is not null; } ```

1. Use x:Bind for compiled bindings — better performance and compile-time checking than {Binding}:

``xml <TextBlock Text="{x:Bind ViewModel.Title, Mode=OneWay}"/> ``

1. Wire DI through `Host.CreateDefaultBuilder` — register services, ViewModels, and views. Resolve via App.GetService<T>().
2. Implement navigation service — map ViewModels to Pages by convention. See references/patterns.md for the full pattern.
3. Handle Windows App SDK features — windowing (AppWindow), custom title bar, app lifecycle, notifications.
4. Always set `XamlRoot` when showing ContentDialog — omitting this causes silent failures.
5. Validate on Windows targets — behavior depends on runtime, packaging model, and Windows version.

Deliver

• modern Windows UI code with clear platform boundaries
• explicit deployment and packaging assumptions
• MVVM pattern with testable ViewModels
• cleaner interop between shared and Windows-specific layers

Validate

• WinUI is chosen for a real product reason, not defaulted to
• Windows App SDK dependencies are explicit in the project file
• packaging and runtime assumptions are tested on target
• x:Bind is used for compiled bindings throughout
• navigation and ContentDialog both work with correct XamlRoot
• custom title bar renders correctly on Windows 10 and 11

References

Related skills