Tim Van Wassenhove

Yesterday i demonstrated how attached properties can be used to invoke commands on specific key presses (and releases). With the aid of System.Windows.Interactivity.Behavior we can implement a true behavior and we get an extension point to do the required cleanup.

<grid>
 <interactivity:Interaction.Behaviors>
  <inf:KeyBehavior>
   <inf:KeyBehavior.DownKeyCommands>
    <inf:KeyCommandName Key="Right" CommandName="PlayerRight"  />
    <inf:KeyCommandName Key="Left" CommandName="PlayerLeft" />
    <inf:KeyCommandName Key="Up" CommandName="PlayerUp" />
    <inf:KeyCommandName Key="Down" CommandName="PlayerDown" />
   </inf:KeyBehavior.DownKeyCommands>
  </inf:KeyBehavior>
 </interactivity:Interaction.Behaviors>
 ...
</grid>

The behavior implementation is the same as yesterday, only this time we thankfully override the OnAttached and OnDetaching methods:

public class KeyBehavior : Behavior<frameworkElement>
{
 public List<keyCommandName> DownKeyCommands { get; set; }
 public List<keyCommandName> UpKeyCommands { get; set; }

 public KeyBehavior()
  : base()
 {
  DownKeyCommands = new List<keyCommandName>();
  UpKeyCommands = new List<keyCommandName>();
 }

 protected override void OnAttached()
 {
  base.OnAttached();
  SubscribeToKeyEvents();
 }

 protected override void OnDetaching()
 {
  UnsubscribeFromKeyEvents();
  base.OnDetaching();
 }

 void SubscribeToKeyEvents()
 {
  AssociatedObject.KeyDown += AssociatedObject_KeyDown;
  AssociatedObject.KeyUp += AssociatedObject_KeyUp;
 }

 void UnsubscribeFromKeyEvents()
 {
  AssociatedObject.KeyDown -= AssociatedObject_KeyDown;
  AssociatedObject.KeyUp -= AssociatedObject_KeyUp;
 }

 ...