How do you handle navigation lifecycle and prevent back navigation in Shell?

Implement IQueryAttributable for parameter handling, and override OnNavigating/OnNavigated or handle Shell.Navigating to inspect or cancel navigation (e.g., unsaved changes). Set args.Cancel() in the Navigating event, or use OnBackButtonPressed on a page to intercept hardware back.

protected override void OnNavigating(ShellNavigatingEventArgs args)
{
    if (HasUnsavedChanges && args.CanCancel)
        args.Cancel();
    base.OnNavigating(args);
}