dotnet-wpf-modern

What this skill does

# dotnet-wpf-modern

WPF on .NET 8+: Host builder and dependency injection, MVVM with CommunityToolkit.Mvvm source generators, hardware-accelerated rendering improvements, modern C# patterns (records, primary constructors, pattern matching), Fluent theme (.NET 9+), system theme detection, and what changed from .NET Framework WPF.

**Version assumptions:** .NET 8.0+ baseline (current LTS). TFM `net8.0-windows`. .NET 9 features (Fluent theme) explicitly marked.

**Scope boundary:** This skill owns WPF on modern .NET patterns: Host builder, MVVM Toolkit, performance, modern C#, theming. Migration from .NET Framework to .NET 8+ is owned by [skill:dotnet-wpf-migration]. Desktop testing is owned by [skill:dotnet-ui-testing-core].

**Out of scope:** WPF .NET Framework patterns (legacy) -- this skill covers .NET 8+ only. Migration guidance -- see [skill:dotnet-wpf-migration]. Desktop testing -- see [skill:dotnet-ui-testing-core]. General Native AOT patterns -- see [skill:dotnet-native-aot]. UI framework selection -- see [skill:dotnet-ui-chooser].

Cross-references: [skill:dotnet-ui-testing-core] for desktop testing, [skill:dotnet-winui] for WinUI 3 patterns, [skill:dotnet-wpf-migration] for migration guidance, [skill:dotnet-native-aot] for general AOT, [skill:dotnet-ui-chooser] for framework selection, [skill:dotnet-accessibility] for accessibility patterns (AutomationProperties, AutomationPeer, UI Automation).

---

## .NET 8+ Differences

WPF on .NET 8+ is a significant modernization from .NET Framework WPF. The project format, DI pattern, language features, and runtime behavior have all changed.

### New Project Template

```xml
<!-- MyWpfApp.csproj (SDK-style) -->
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net8.0-windows</TargetFramework>
    <UseWPF>true</UseWPF>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.*" />
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.*" />
  </ItemGroup>
</Project>
```

**Key differences from .NET Framework WPF:**
- SDK-style `.csproj` (no `packages.config`, no `AssemblyInfo.cs`)
- Nullable reference types enabled by default
- Implicit usings enabled
- NuGet `PackageReference` format (not `packages.config`)
- No `App.config` for DI -- use Host builder
- `dotnet publish` produces a single deployment artifact
- Side-by-side .NET installation (no machine-wide framework dependency)

### Host Builder Pattern

Modern WPF apps use the generic host for dependency injection, configuration, and logging -- replacing the legacy `ServiceLocator` or manual DI approaches.

```csharp
// App.xaml.cs
public partial class App : Application
{
    private readonly IHost _host;

    public App()
    {
        _host = Host.CreateDefaultBuilder()
            .ConfigureAppConfiguration((context, config) =>
            {
                config.AddJsonFile("appsettings.json", optional: true);
            })
            .ConfigureServices((context, services) =>
            {
                // Services
                services.AddSingleton<INavigationService, NavigationService>();
                services.AddSingleton<IProductService, ProductService>();
                services.AddSingleton<ISettingsService, SettingsService>();

                // HTTP client
                services.AddHttpClient("api", client =>
                {
                    client.BaseAddress = new Uri(
                        context.Configuration["ApiBaseUrl"] ?? "https://api.example.com");
                });

                // ViewModels
                services.AddTransient<MainViewModel>();
                services.AddTransient<ProductListViewModel>();
                services.AddTransient<SettingsViewModel>();

                // Windows and pages
                services.AddSingleton<MainWindow>();
            })
            .Build();
    }

    protected override async void OnStartup(StartupEventArgs e)
    {
        await _host.StartAsync();

        var mainWindow = _host.Services.GetRequiredService<MainWindow>();
        mainWindow.Show();

        base.OnStartup(e);
    }

    protected override async void OnExit(ExitEventArgs e)
    {
        await _host.StopAsync();
        _host.Dispose();

        base.OnExit(e);
    }

    public static T GetService<T>() where T : class
    {
        var app = (App)Application.Current;
        return app._host.Services.GetRequiredService<T>();
    }
}
```

---

## MVVM Toolkit

CommunityToolkit.Mvvm (Microsoft MVVM Toolkit) is the recommended MVVM framework for modern WPF. It uses source generators to eliminate boilerplate.

```csharp
// ViewModels/ProductListViewModel.cs
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;

public partial class ProductListViewModel : ObservableObject
{
    private readonly IProductService _productService;

    public ProductListViewModel(IProductService productService)
    {
        _productService = productService;
    }

    [ObservableProperty]
    [NotifyCanExecuteChangedFor(nameof(SearchCommand))]
    private string _searchTerm = "";

    [ObservableProperty]
    private ObservableCollection<Product> _products = [];

    [ObservableProperty]
    private bool _isLoading;

    [RelayCommand]
    private async Task LoadProductsAsync(CancellationToken ct)
    {
        IsLoading = true;
        try
        {
            var items = await _productService.GetProductsAsync(ct);
            Products = new ObservableCollection<Product>(items);
        }
        finally
        {
            IsLoading = false;
        }
    }

    [RelayCommand(CanExecute = nameof(CanSearch))]
    private async Task SearchAsync(CancellationToken ct)
    {
        var results = await _productService.SearchAsync(SearchTerm, ct);
        Products = new ObservableCollection<Product>(results);
    }

    private bool CanSearch() => !string.IsNullOrWhiteSpace(SearchTerm);
}
```

### XAML Binding with MVVM Toolkit

```xml
<Window x:Class="MyApp.Views.ProductListWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:vm="clr-namespace:MyApp.ViewModels"
        d:DataContext="{d:DesignInstance vm:ProductListViewModel}">

    <DockPanel>
        <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Margin="16">
            <TextBox Text="{Binding SearchTerm, UpdateSourceTrigger=PropertyChanged}"
                     Width="300" Margin="0,0,8,0" />
            <Button Content="Search" Command="{Binding SearchCommand}" />
        </StackPanel>

        <ListBox ItemsSource="{Binding Products}" Margin="16">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal" Margin="4">
                        <TextBlock Text="{Binding Name}" FontWeight="Bold" Margin="0,0,12,0" />
                        <TextBlock Text="{Binding Price, StringFormat='{}{0:C}'}" Foreground="Gray" />
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </DockPanel>
</Window>
```

**Key source generator attributes:**
- `[ObservableProperty]` -- generates property with `INotifyPropertyChanged` from a backing field
- `[RelayCommand]` -- generates `ICommand` from a method (supports async, cancellation, `CanExecute`)
- `[NotifyPropertyChangedFor]` -- raises `PropertyChanged` for dependent properties
- `[NotifyCanExecuteChangedFor]` -- re-evaluates command `CanExecute` when property changes

---

## Performance

WPF on .NET 8+ delivers significant performance improvements over .NET Framework WPF.

### Hardware-Accelerated Rendering

- **DirectX 11 rendering path** is the default on .NET 8+ (up from DirectX 9