Tim Van Wassenhove

If you look at my KeyBehavior you notice that it is doing two things: register for events so that the behavior can be triggered and handle the actual command invocation. In order to enhance reuse we can refactor this KeyBehavior in a KeyTrigger and an InvokeCommandAction. Well, we’re not going to do that, because they exist already in the silverlight sdk

A shortcoming of the InvokeCommandAction is that it can only invoke commands on the FrameworkElement itself, thus we write a custom implementation that finds commands on the DataContext instead:

public class InvokeCommandAction : TriggerAction<FrameworkElement>
{
 public string CommandName { get; set; }

 protected override void Invoke(object parameter)
 {
  var viewModel = AssociatedObject.DataContext;
  GetCommandAndExecuteIt(viewModel, CommandName);
 }

 void GetCommandAndExecuteIt(object viewModel, string commandName)
 {
  var command = viewModel.GetPropertyValue<ICommand>(commandName);
  if(command.CanExecute(null)) command.Execute(null);
 }
}

And now we can drag this action on our design surface in Blend and select a trigger that goes with it:

All we have to do is choose the Key and Command to invoke:

In XAML this looks like:

<interactivity:Interaction.Triggers>
 <ii:KeyTrigger Key="Right">
  <inf:InvokeCommandAction CommandName="PlayerRight"/>
 </ii:KeyTrigger>
 <ii:KeyTrigger Key="Left">
  <inf:InvokeCommandAction CommandName="PlayerLeft"/>
 </ii:KeyTrigger>
 <ii:KeyTrigger Key="Up">
  <inf:InvokeCommandAction CommandName="PlayerUp"/>
 </ii:KeyTrigger>
 <ii:KeyTrigger Key="Down">
  <inf:InvokeCommandAction CommandName="PlayerDown"/>
 </ii:KeyTrigger>
</interactivity:Interaction.Triggers>

I guess this ends our exploration of the behavior features in Silverlight.