Navigation, windows and dialogs

Modal windows with ownership and results, a navigation service that a view model can use without referencing WPF, frame and tab navigation, and window lifetime rules.

Windows and modal dialogs

// the dialog stays in front, and we read the result afterwards
var dialog = new CustomerEditWindow { Owner = this, DataContext = new CustomerEditViewModel(id) };

if (dialog.ShowDialog() == true)
    await _orders.ReloadAsync();

// and inside the dialog
private void OnSave(object sender, RoutedEventArgs e)
{
    if (!_viewModel.Validate()) return;
    DialogResult = true;         // also closes the window
}

• Set Owner before ShowDialog, or the dialog can disappear behind the main window.
• DialogResult only works on a window shown with ShowDialog; setting it on a modeless window throws.
• A view model should not open windows directly. Inject a navigation or dialog service so the view model stays testable.
• Closing the main window ends the application by default (ShutdownMode). Change it only if you add a tray icon or a splash window.

A navigation service

public interface IDialogService
{
    bool? ShowCustomerEditor(Guid customerId);
    Task<bool> ConfirmAsync(string title, string message);
}

public sealed class DialogService : IDialogService
{
    public bool? ShowCustomerEditor(Guid customerId)
    {
        var vm = new CustomerEditViewModel(customerId);
        var window = new CustomerEditWindow { DataContext = vm, Owner = Application.Current.MainWindow };
        return window.ShowDialog();
    }

    public Task<bool> ConfirmAsync(string title, string message)
    {
        var result = MessageBox.Show(Application.Current.MainWindow, message, title,
            MessageBoxButton.OKCancel, MessageBoxImage.Question) == MessageBoxResult.OK;
        return Task.FromResult(result);
    }
}

// the view model depends on the abstraction, so it can be tested with a fake
public sealed class OrdersViewModel
{
    private readonly IDialogService _dialogs;

    public OrdersViewModel(IDialogService dialogs) => _dialogs = dialogs;

    public async Task EditAsync()
    {
        if (Selected is null) return;
        if (_dialogs.ShowCustomerEditor(Selected.Id) == true)
            await ReloadAsync();
    }
}

For a multi-view application, either set a single ContentControl whose content is the current view model, or use a Frame with pages. The ContentControl plus data templates keeps the view model in charge; the Frame gives you a journal and back navigation for free.

Tabs, frames and lifetime

<!-- one content host, a template that picks the view for the current view model -->
<Window.Resources>
  <DataTemplate DataType="{x:Type vm:OrdersViewModel}">
    <views:OrdersView />
  </DataTemplate>
  <DataTemplate DataType="{x:Type vm:SettingsViewModel}">
    <views:SettingsView />
  </DataTemplate>
</Window.Resources>

<ContentControl Content="{Binding Current}" />

<!-- a TabControl keeps every tab alive; that is a memory decision, not just a layout one -->
<TabControl ItemsSource="{Binding Tabs}" SelectedItem="{Binding SelectedTab}" />

FAQ

Related

Validation, converters and input handling Asynchronous work and UI responsiveness

Last refreshed 2026-09-18.