Handling the window closing event with WPF / MVVM Light Toolkit

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I would simply associate the handler in the View constructor:

MyWindow() 
{
    // Set up ViewModel, assign to DataContext etc.
    Closing += viewModel.OnWindowClosing;
}

Then add the handler to the ViewModel:

using System.ComponentModel;

public void OnWindowClosing(object sender, CancelEventArgs e) 
{
   // Handle closing logic, set e.Cancel as needed
}

In this case, you gain exactly nothing except complexity by using a more elaborate pattern with more indirection (5 extra lines of XAML plus Command pattern).

The “zero code-behind” mantra is not the goal in itself, the point is to decouple ViewModel from the View. Even when the event is bound in code-behind of the View, the ViewModel does not depend on the View and the closing logic can be unit-tested.

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