How can I bind a command to a local event?

Question

I have a form that should capture KeyDown/KeyUp events.

This code fails with NRE, because it looks for KeyDown control on my current view:

this.BindCommand(ViewModel, vm => vm.KeyDown, "KeyDown");

What I've done is created wrapper class that has form as a property, so I can use this overload:

this.BindCommand(ViewModel, vm => vm.KeyDown, v => v.Form, "KeyDown");

While it works, it seems like a hack to me. Is there a proper way to bind to local events?

Answer 1

That's the right way to do it if you're using BindCommand. If you want to get rid of the string and you're using ReactiveUI.Events, you could also do:

this.Form.Events().KeyDown
    .InvokeCommand(this, x => x.ViewModel.KeyDown);

As an aside, "KeyDown" isn't a very MVVM'y command. I'd write your key => command mappings at the View layer, like this (coding via TextArea, ignore syntax bugs):

this.Form.Events().KeyDown
    .Where(x => x.Key == Key.C && (x.Modifier & Modifier.Ctrl))
    .InvokeCommand(this, x => x.ViewModel.CopyText;

Answer 2

I realize I'm really late to this particular party, but since I've been working on something similar, this is the approach I took, based on Paul's advice:

var keyDownSub= Observable.FromEventPattern<KeyEventHandler, KeyEventArgs>(
            ev => txtbxCommandLine.KeyDown += ev,
            ev => txtbxCommandLine.KeyDown -= ev
            ).Select(x => x.EventArgs)
            .Where(x => 
                x.KeyCode.ToString().ToUpper().Equals("RETURN") 
                && (_returnKeyPressed || x.Alt || x.Control))
            .InvokeCommand(_mainViewModel.ProcessCommandLine);

This seems to work perfectly fine in WinForms, if it is a bit more verbose than it would be in WPF.