How to use disposable view models in WPF?

Question

How do I ensure view models are properly disposed of if they reference unmanaged resources or have event handlers such as handling elapsed on a dispatcher timer. In the first case, a finaliser is an option, although not ideal, but in the latter, it will never be called. How can we tell when there is no longer a view attached to the view model.

Answer 1

One possible, although not perfect solution:

Implement IDisposable on the View Model, then use this extension method in the constructor of the view.

    public static void HandleDisposableViewModel(this FrameworkElement Element)
    {
        Action Dispose = () =>
            {
                var DataContext = Element.DataContext as IDisposable;
                if (DataContext != null)
                {
                    DataContext.Dispose();
                }
            };
        Element.Unloaded += (s, ea) => Dispose();
        Element.Dispatcher.ShutdownStarted += (s, ea) => Dispose();
    }

Answer 2

I accomplished this by doing the following:

1. Removing the StartupUri property from App.xaml.

2. Defining my App class as follows:

   public partial class App : Application
   {
       public App()
       {
           IDisposable disposableViewModel = null;
   
           //Create and show window while storing datacontext
           this.Startup += (sender, args) =>
           {
               MainWindow = new MainWindow();
               disposableViewModel = MainWindow.DataContext as IDisposable;
   
               MainWindow.Show();
           };
   
           //Dispose on unhandled exception
           this.DispatcherUnhandledException += (sender, args) => 
           { 
               if (disposableViewModel != null) disposableViewModel.Dispose(); 
           };
   
           //Dispose on exit
           this.Exit += (sender, args) =>
           { 
               if (disposableViewModel != null) disposableViewModel.Dispose(); 
           };
       }
   }