Skills
skills/rudironsoni/dotnet-harness-plugin/dotnet-wpf-modern

dotnet-wpf-modern

SKILL.md

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

  • WPF .NET 8+ project setup (SDK-style)
  • Host builder and dependency injection
  • MVVM with CommunityToolkit.Mvvm source generators
  • Fluent theme (.NET 9+) and system theme detection
  • Hardware-accelerated rendering improvements
  • Modern C# patterns (records, primary constructors, pattern matching)

Out of scope

  • WPF .NET Framework patterns (legacy)
  • 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


<!-- 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>

```text

**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>();
    }
}

```text

---

## 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);
}

```text

### 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>

```text

**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 on .NET Framework)
- **GPU-accelerated text rendering** improves text clarity and reduces CPU usage for text-heavy UIs
- **Reduced GC pressure** from runtime improvements (dynamic PGO, on-stack replacement)

### Startup Time

- **ReadyToRun (R2R)** -- pre-compiled assemblies reduce JIT overhead at startup
- **Tiered compilation** -- fast startup with progressive optimization
- **Trimming readiness** -- `.NET 8+` WPF supports IL trimming for smaller deployment size

```xml

<!-- Enable trimming for smaller deployment -->
<PropertyGroup>
  <PublishTrimmed>true</PublishTrimmed>
  <TrimMode>partial</TrimMode>
  <!-- WPF apps need partial trim mode due to reflection usage -->
</PropertyGroup>

```text

**Trimming caveat:** WPF relies heavily on XAML reflection for data binding and resource resolution. Use `TrimMode=partial` (not `full`) and test thoroughly. Compiled bindings and `x:Type` references are safer than string-based bindings for trimming.

### Memory and GC

- **Frozen object heap** (.NET 8) -- static strings and singleton allocations placed on non-collected heap segments
- **Dynamic PGO** -- runtime profiles guide JIT optimizations for hot paths
- **Reduced working set** -- .NET 8 runtime uses less baseline memory than .NET Framework CLR

### Expected Improvements

WPF on .NET 8 delivers measurable improvements over .NET Framework 4.8 across key metrics. Exact numbers depend on workload, hardware, and application complexity -- always benchmark your own scenarios:

- **Cold startup** -- significantly faster due to ReadyToRun, tiered compilation, and reduced framework initialization overhead
- **UI virtualization** -- improved rendering pipeline and GC reduce time for large ItemsControls (ListBox, DataGrid)
- **GC pauses** -- shorter and less frequent Gen2 collections from .NET 8 GC improvements (Dynamic PGO, frozen object heap, pinned object heap)
- **Memory footprint** -- lower baseline working set compared to .NET Framework CLR

---

## Modern C#

.NET 8+ WPF projects can use the latest C# language features. These patterns reduce boilerplate and improve code clarity.

### Records for Data Models

```csharp

// Immutable data models
public record Product(string Name, decimal Price, string Category);

// Records with computed properties
public record ProductViewModel(Product Product)
{
    public string DisplayPrice => Product.Price.ToString("C");
    public string Summary => $"{Product.Name} - {DisplayPrice}";
}

```text

### Primary Constructors in Services

```csharp

// Service with primary constructor (C# 12)
public class ProductService(HttpClient httpClient, ILogger<ProductService> logger)
    : IProductService
{
    public async Task<IReadOnlyList<Product>> GetProductsAsync(CancellationToken ct)
    {
        logger.LogInformation("Fetching products");
        var response = await httpClient.GetAsync("/products", ct);
        response.EnsureSuccessStatusCode();
        return await response.Content.ReadFromJsonAsync<List<Product>>(ct) ?? [];
    }
}

```json

### Pattern Matching in Converters

```csharp

// Modern converter using pattern matching (C# 11+)
public class StatusToColorConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value switch
        {
            OrderStatus.Pending => Brushes.Orange,
            OrderStatus.Processing => Brushes.Blue,
            OrderStatus.Shipped => Brushes.Green,
            OrderStatus.Cancelled => Brushes.Red,
            _ => Brushes.Gray
        };
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        => throw new NotSupportedException();
}

```text

### Collection Expressions

```csharp

// C# 12 collection expressions
[ObservableProperty]
private ObservableCollection<Product> _products = [];

// In methods
List<string> categories = ["Electronics", "Clothing", "Books"];

```text

---

## Theming

### Fluent Theme (.NET 9+)

.NET 9 introduces the Fluent theme for WPF, providing modern Windows 11-style visuals. It applies rounded corners, updated control templates, and Mica/Acrylic backdrop support.

```xml

<!-- App.xaml: enable Fluent theme (.NET 9+) via ThemeMode property -->
<Application x:Class="MyApp.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             ThemeMode="System"
             StartupUri="MainWindow.xaml">
</Application>

```xml

Or in code-behind:

```csharp

// App.xaml.cs: set theme programmatically (.NET 9+)
Application.Current.ThemeMode = ThemeMode.System; // or ThemeMode.Light / ThemeMode.Dark

// Per-window theming is also supported
mainWindow.ThemeMode = ThemeMode.Dark;

```text

**ThemeMode values:**
- `None` -- classic WPF look (no Fluent styling)
- `Light` -- Fluent theme with light colors
- `Dark` -- Fluent theme with dark colors
- `System` -- follow Windows system light/dark theme setting

**Fluent theme includes:**
- Rounded corners on buttons, text boxes, and list items
- Updated color palette aligned with Windows 11 design language
- Mica and Acrylic backdrop support (Windows 11)
- Accent color integration with Windows system settings
- Dark/light mode following system theme

### System Theme Detection

Detect and respond to the Windows system light/dark theme:

```csharp

// Detect system theme
public static bool IsDarkTheme()
{
    using var key = Microsoft.Win32.Registry.CurrentUser.OpenSubKey(
        @"Software\Microsoft\Windows\CurrentVersion\Themes\Personalize");
    var value = key?.GetValue("AppsUseLightTheme");
    return value is int i && i == 0;
}

// Listen for theme changes
SystemEvents.UserPreferenceChanged += (sender, args) =>
{
    if (args.Category == UserPreferenceCategory.General)
    {
        // Theme may have changed; re-read and apply
        ApplyTheme(IsDarkTheme() ? AppTheme.Dark : AppTheme.Light);
    }
};

```text

### Custom Themes

For pre-.NET 9 apps or custom branding, use resource dictionaries:

```xml

<!-- Themes/DarkTheme.xaml -->
<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <SolidColorBrush x:Key="WindowBackground" Color="#1E1E1E" />
    <SolidColorBrush x:Key="TextForeground" Color="#FFFFFF" />
    <SolidColorBrush x:Key="AccentBrush" Color="#0078D7" />
</ResourceDictionary>

```text

```csharp

// Switch themes at runtime
public void ApplyTheme(AppTheme theme)
{
    var themeUri = theme switch
    {
        AppTheme.Dark => new Uri("Themes/DarkTheme.xaml", UriKind.Relative),
        AppTheme.Light => new Uri("Themes/LightTheme.xaml", UriKind.Relative),
        _ => throw new ArgumentOutOfRangeException(nameof(theme))
    };

    Application.Current.Resources.MergedDictionaries.Clear();
    Application.Current.Resources.MergedDictionaries.Add(
        new ResourceDictionary { Source = themeUri });
}

```text

---

## Agent Gotchas

1. **Do not use .NET Framework WPF patterns in .NET 8+ projects.** Avoid `App.config` for DI (use Host builder), `packages.config` (use `PackageReference`), `ServiceLocator` pattern (use constructor injection), and `AssemblyInfo.cs` (use `<PropertyGroup>` properties).
2. **Do not use deprecated WPF APIs.** `BitmapEffect` (replaced by `Effect`/`ShaderEffect`), `DrawingContext.PushEffect` (removed), and `VisualBrush` tile modes with hardware acceleration disabled are obsolete.
3. **Do not mix `{Binding}` and manual `INotifyPropertyChanged` when using MVVM Toolkit.** Use `[ObservableProperty]` source generators consistently. Mixing approaches causes subtle binding update bugs.
4. **Do not use `Dispatcher.Invoke` from async code.** In async methods, `await` automatically marshals back to the UI thread (the default `ConfigureAwait(true)` behavior). `Dispatcher.Invoke`/`BeginInvoke` is still appropriate from non-async contexts (timers, COM callbacks, native interop).
5. **Do not set `TrimMode=full` for WPF apps.** WPF uses XAML reflection extensively. Use `TrimMode=partial` and test all views after trimming to catch missing types.
6. **Do not forget the Host builder lifecycle.** Call `_host.StartAsync()` in `OnStartup` and `_host.StopAsync()` in `OnExit`. Forgetting lifecycle management causes DI-registered `IHostedService` instances to never start or stop.
7. **Do not hardcode colors when using Fluent theme.** Reference theme resources (`{DynamicResource SystemAccentColor}`) to maintain compatibility with light/dark mode and system accent color changes.

---

## Prerequisites

- .NET 8.0+ with Windows desktop workload
- TFM: `net8.0-windows` (no Windows SDK version needed for WPF)
- Visual Studio 2022+, VS Code with C# Dev Kit, or JetBrains Rider
- For Fluent theme: .NET 9+

---

## References

- [WPF on .NET Documentation](https://learn.microsoft.com/en-us/dotnet/desktop/wpf/)
- [CommunityToolkit.Mvvm](https://learn.microsoft.com/en-us/dotnet/communitytoolkit/mvvm/)
- [WPF Fluent Theme (.NET 9)](https://learn.microsoft.com/en-us/dotnet/desktop/wpf/whats-new/net90)
- [Microsoft.Extensions.Hosting](https://learn.microsoft.com/en-us/dotnet/core/extensions/generic-host)
- [WPF Performance](https://learn.microsoft.com/en-us/dotnet/desktop/wpf/advanced/optimizing-performance)
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