Agent Skills: View-ViewModel Wiring — Prism 9

View-ViewModel Wiring — Prism 9

Applies when Prism 9 is the active MVVM framework. Mappings.xaml is NOT used with Prism.

Composition style: View First Composition + Stateful ViewModel (RegisterForNavigation + IRegionManager). See docs/TERMINOLOGY.md.

Registration in App.xaml.cs

protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
    containerRegistry.RegisterForNavigation<HomeView, HomeViewModel>();
    containerRegistry.RegisterForNavigation<SettingsView, SettingsViewModel>();
}

Shell — Region Definition

<Window x:Class="MyApp.MainWindow"
        xmlns:prism="http://prismlibrary.com/">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>

        <StackPanel Grid.Row="0" Orientation="Horizontal" Margin="10">
            <Button Content="Home" Command="{Binding NavigateCommand}"
                    CommandParameter="HomeView" Margin="5" />
            <Button Content="Settings" Command="{Binding NavigateCommand}"
                    CommandParameter="SettingsView" Margin="5" />
        </StackPanel>

        <!-- Region instead of ContentControl + DataTemplate -->
        <ContentControl Grid.Row="1"
                        prism:RegionManager.RegionName="ContentRegion" />
    </Grid>
</Window>

Shell ViewModel — Navigation

namespace MyApp.ViewModels;

public class MainWindowViewModel : BindableBase
{
    private readonly IRegionManager _regionManager;

    public MainWindowViewModel(IRegionManager regionManager)
    {
        _regionManager = regionManager;
    }

    private DelegateCommand<string>? _navigateCommand;
    public DelegateCommand<string> NavigateCommand =>
        _navigateCommand ??= new DelegateCommand<string>(ExecuteNavigate);

    private void ExecuteNavigate(string viewName)
    {
        _regionManager.RequestNavigate("ContentRegion", viewName);
    }
}

NavigationParameters

private void NavigateToDetail(int userId)
{
    var parameters = new NavigationParameters
    {
        { "userId", userId },
        { "mode", "edit" }
    };

    _regionManager.RequestNavigate("ContentRegion", "DetailView", parameters);
}

INavigationAware — Lifecycle Callbacks

namespace MyApp.ViewModels;

public class HomeViewModel : BindableBase, INavigationAware
{
    // Called when navigated to this View
    public void OnNavigatedTo(NavigationContext navigationContext)
    {
        if (navigationContext.Parameters.ContainsKey("userId"))
        {
            var userId = navigationContext.Parameters.GetValue<int>("userId");
            LoadUser(userId);
        }
    }

    // Whether to reuse existing instance
    public bool IsNavigationTarget(NavigationContext navigationContext)
    {
        return true;
    }

    // Called when navigating away
    public void OnNavigatedFrom(NavigationContext navigationContext)
    {
        // Cleanup logic
    }
}

IConfirmNavigationRequest — Cancel Navigation

public class EditViewModel : BindableBase, IConfirmNavigationRequest
{
    public void ConfirmNavigationRequest(
        NavigationContext navigationContext,
        Action<bool> continuationCallback)
    {
        if (HasUnsavedChanges)
        {
            var result = MessageBox.Show(
                "You have unsaved changes. Navigate away?",
                "Confirm", MessageBoxButton.YesNo);
            continuationCallback(result == MessageBoxResult.Yes);
        }
        else
        {
            continuationCallback(true);
        }
    }

    public void OnNavigatedTo(NavigationContext ctx) { }
    public bool IsNavigationTarget(NavigationContext ctx) => true;
    public void OnNavigatedFrom(NavigationContext ctx) { }
}

Comparison with CommunityToolkit.Mvvm

| Item | CommunityToolkit.Mvvm | Prism 9 | |---|---|---| | View-VM mapping | DataTemplate in Mappings.xaml | RegisterForNavigation<V, VM>() | | Navigation | Replace CurrentViewModel property | IRegionManager.RequestNavigate() | | VM auto-wiring | DataTemplate DataType matching | DI container auto-resolve | | Parameters | Manual property assignment | NavigationParameters (type-safe) | | Lifecycle | None | INavigationAware, IConfirmNavigationRequest | | Hosting control | ContentControl + Binding | ContentControl + RegionManager.RegionName |