Keybinding a RelayCommand

Question

I'm using the RelayCommand in my app. It's great for putting the code in the viewmodel, but how do I bind keystrokes to my command?

RoutedUICommand has its InputGestures property, which makes the command automatically be invoked when I press the keystroke. (As an added bonus, it even makes the keystroke display in the MenuItem.) Unfortunately, there's no reusable interface for RoutedUICommand's extra properties, so I can't make a RelayUICommand that gets the same magic.

I've already tried using InputBindings:

<Window.InputBindings>     <KeyBinding Key="PageUp" Command="{Binding SelectPreviousLayerCommand}"/> </Window.InputBindings> 

But that gets me a runtime exception, because KeyBinding.Command isn't a dependency property. (Actually, what it complains about is that KeyBinding isn't even a DependencyObject.) And since my RelayCommand is a property on my ViewModel (as opposed to the static field that RoutedUICommand is designed for), databinding is the only way I know of to reference it from XAML.

How have you guys solved this? What's the best way to bind a keystroke to a RelayCommand?

Answer 1

I don't think you can do this from XAML, for exactly the reasons you describe.

I ended up doing it in the code-behind. Although it's code, it's only a single line of code, and still rather declarative, so I can live with it. However, I'd really hope that this is solved in the next version of WPF.

Here's a sample line of code from one of my projects:

this.InputBindings.Add(new KeyBinding(     ((MedicContext)this.DataContext).SynchronizeCommand,     new KeyGesture(Key.F9))); 

SynchronizeCommand in this case is an instance of RelayCommand, and (obviously) F9 triggers it.

Answer 2

The Command property of the KeyBinding class doesn't support data binding. This issue is going to be solved in .NET 4.0 and you should be able to see it in the coming .NET 4.0 Beta 2 version.