AGIBuild/dotnet-wpf-modern

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).

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.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>

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.

// 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.

// 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

<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 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

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

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

// 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}";
}

Primary Constructors in Services

// 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) ?? [];
    }
}

Pattern Matching in Converters

// 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();
}

Collection Expressions

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

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

---

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.

<!-- 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>

Or in code-behind:

// 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;

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:

// 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);
    }
};

Custom Themes

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

<!-- 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>

// 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 });
}

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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.

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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+

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References

• WPF on .NET Documentation
• CommunityToolkit.Mvvm
• WPF Fluent Theme (.NET 9)
• Microsoft.Extensions.Hosting
• WPF Performance