WPF MVVM Code Behind Best Practices

Question

I'm a student learning C# with WPF using the MVVM pattern. Recently I have been working on a [art of my application (a custom splash screen) that should not be closed when I don't want it to. I have been searching the web for a good way of doing this without code-behind. Unfortunately after days I still did not find a satisfying way. Then I came to think of a way to do it myself, with help of just one line of code in the constructor of my view. It still makes my code testable and decouples the code from the View. The question is, is there a better way of doing what I'm trying to do:

My interface for my ViewModel

public interface IPreventCloseViewModel
{
    bool PreventClose { get; set; }
}

The extension for the View

public static class PreventCloseViewModelExtension
{
    /// <summary>
    /// Use this extension method in the constructor of the view.
    /// </summary>
    /// <param name="element"></param>
    public static void PreventCloseViewModel(this Window element)
    {
        var dataContext = element.DataContext as IDisposable;
        if (dataContext is IPreventCloseViewModel)
        {
            element.Closing += delegate(object sender, CancelEventArgs args)
                                   {
                                       if (dataContext is IPreventCloseViewModel)
                                       {
                                           args.Cancel = (dataContext as IPreventCloseViewModel).PreventClose;
                                       }
                                   };
        }
    }
}

The code-behind for the View

public partial class SplashScreen
{
    public SplashScreen()
    {
        InitializeComponent();
        this.PreventCloseViewModel();
    }
}

Answer 1

MVVM does not mean that you cannot use Code-Behind.

MVVM means that your application logic should not be tied to UI elements.

You can perfectly well handle events in code behind (such as Window.Closing), and "send messages" or execute methods in the ViewModel to react to that.

Here, you are not breaking MVVM by placing the event handler in code behind. You would be breaking MVVM if you were placing the logic that determines whether the application can be closed in code behind. That is a responsibility of the application logic, and the application logic lives in ViewModels, not Views.