How should I handle multiple events per control w/command pattern using MVVM in Silverlight?

Question

Is anyone using the SLExtensions command pattern (http://www.codeplex.com/SLExtensions) for associating commands to Silverlight control events? From what I've seen, you can only attach a command for one event per control. For example, you can only add a click event for a button, a keydown event for a textbox, etc.

What if I wanted to add multiple events per control? For example, what if I wanted to add commands for both Click and Drop events for a button. Out of the box there does not seem to be a way to handle this with the SLExtensions code.

BTW, this is in a Model-View-ViewModel (MVVM) context.

Answer 1

Which events you wire upto in the XAML are a little limited, but but there's nothing to stop you doing it in the code behind/view model if it's not naturally supported by SLExtensions.

if (action == dropped)
{
  Commands.Dropped.Execute();
else
{
  Commands.Clicked.Execute();
}

Or whatever... if I've misunderstood you, some sample code of what you want to do would be helpful.

Answer 2

dwynne - You're absolutely correct. I could handle the drop event using the code you specified. However, I would still have to implement the event handler in my code-behind then call my ViewModel from there. I'm trying to adhere to MVVM by attempting the eliminate coding event handlers into my code-behind. Instead, I would like to wire-up my XAML to my ViewModel directly by using the attached commands.

The SLExtensions library allows you to do this but (from what I've experienced) only allows one event per control (Click for button, keydown for textbox, etc). For any non-trivial application this is not sufficient and your MVVM implementation breaks down.

Sorry for not using the comments area but 300 characters is a bit limiting. StackOverflow people - you need to up this limit.

Answer 3

I'm not familiar with SLExtensions but in WPF you have the same limit of one command per control, which is associated by the control implementation. If you want a command to execute for another event, you have to wire that yourself. However, there is a solution that doesn't require you to do this wiring in the code behind... attached behaviors. In fact, Caliburn (http://www.codeplex.com/caliburn) does just this with its "Action" concepts. I've not looked at Caliburn in a long time, and have no idea if it's Silverlight compatible, but you can certainly look into how the Actions are codified there and implement your own.