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

I know this question is very old, but I came by this because this type of functionality was just made easier to implement in Silverlight (5). So maybe others will come by here too.

I wrote this simple solution after I could not find what I was looking for. Turned out it was rather simple. It should work in both Silverlight 5 and WPF.

public class KeyToCommandExtension : IMarkupExtension
{
    public string Command { get; set; }
    public Key Key { get; set; }

    private void KeyEvent(object sender, KeyEventArgs e)
    {
        if (Key != Key.None && e.Key != Key) return;

        var target = (FrameworkElement)sender;

        if (target.DataContext == null) return;

        var property = target.DataContext.GetType().GetProperty(Command, BindingFlags.Public | BindingFlags.Instance, null, typeof(ICommand), new Type[0], null);

        if (property == null) return;

        var command = (ICommand)property.GetValue(target.DataContext, null);

        if (command != null && command.CanExecute(Key))
            command.Execute(Key);
    }

    public Delegate ProvideValue(IServiceProvider serviceProvider)
    {
        if (string.IsNullOrEmpty(Command))
            throw new InvalidOperationException("Command not set");

        var targetProvider = (IProvideValueTarget)serviceProvider.GetService(typeof(IProvideValueTarget));

        if (!(targetProvider.TargetObject is FrameworkElement))
            throw new InvalidOperationException("Target object must be FrameworkElement");

        if (!(targetProvider.TargetProperty is EventInfo))
            throw new InvalidOperationException("Target property must be event");

        return Delegate.CreateDelegate(typeof(KeyEventHandler), this, "KeyEvent");
    }

Usage:

Notice that Command is a string and not an bindable ICommand. I know this is not as flexible, but it is cleaner when used, and what you need 99% of the time. Though it should not be a problem to change.