Keyboard events in a WPF MVVM application?

Question

How can I handle the Keyboard.KeyDown event without using code-behind? We are trying to use the MVVM pattern and avoid writing an event handler in code-behind file.

Answer 1

WOW - there's like a thousand answers and here I'm going to add another one..

The really obvious thing in a 'why-didn't-I-realise-this-forehead-slap' kind of way is that the code-behind and the ViewModel sit in the same room so-to-speak, so there is no reason why they're not allowed to have a conversation.

If you think about it, the XAML is already intimately coupled to the ViewModel's API, so you might just as well go and make a dependency on it from the code behind.

The other obvious rules to obey or ignore still applies (interfaces, null checks <-- especially if you use Blend...)

I always make a property in the code-behind like this:

private ViewModelClass ViewModel { get { return DataContext as ViewModelClass; } }

This is the client-code. The null check is for helping control hosting as like in blend.

void someEventHandler(object sender, KeyDownEventArgs e)
{
    if (ViewModel == null) return;
    /* ... */
    ViewModel.HandleKeyDown(e);
}

Handle your event in the code behind like you want to (UI events are UI-centric so it's OK) and then have a method on the ViewModelClass that can respond to that event. The concerns are still seperated.

ViewModelClass
{
    public void HandleKeyDown(KeyEventArgs e) { /* ... */ }
}

All these other attached properties and voodoo is very cool and the techniques are really useful for some other things, but here you might get away with something simpler...