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POWhy doesn't this class handler attached to a tunneling event fire before an instance handler?
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  1. POWhy doesn't this class handler attached to a tunneling event fire before an instance handler?
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    copied!<p>According to <a href="http://msdn.microsoft.com/en-us/library/ms742806.aspx#class_handlers" rel="nofollow">this MSDN article</a> (among others),</p> <blockquote> <p>Class handlers are invoked before any instance listener handlers that are attached to an instance of that class, whenever a routed event reaches an element instance in its route.</p> </blockquote> <p>I'm quite new to <code>RoutedEvent</code>s so there is a chance that I have a mistake in my code, but it seems as though a class handler attached to a <code>RoutedEvent</code> that is declared as <code>RoutingStrategy.Tunnel</code> does <em>not</em> always fire before the instance handlers attached to the same event.</p> <p>In my example below, I have created a <code>TouchButton</code> control class with a tunneling <code>RoutedEvent</code> and a bubbling <code>RoutedEvent</code>. I have registered class handlers for each. I then created an instance of the class in a window and handle each event in the code behind. I attached the same handler for the tunneling event on both the class element and the <code>Grid</code> that contains it. All four handlers display their name in a <code>MessageBox</code> so you can clearly see the order of execution.</p> <ol> <li>Grid Instance PreviewTouch</li> <li>Class TouchButton_PreviewTouch</li> <li>TouchButton Instance PreviewTouch</li> <li>Class TouchButton_Touch</li> <li>TouchButton Instance Touch</li> </ol> <p>This means that if I call <code>e.Handled = true;</code> in the class <code>PreviewTouch</code> event handler, I can stop execution from reaching all of the other event handlers except for the one attached to the <code>Grid</code> element. Is this supposed to be like this, or have I made a mistake somewhere? Otherwise, how can I stop execution from reaching <em>every</em> instance event handler?</p> <p>Here is the class:</p> <pre><code>public class TouchButton : Button { static TouchButton() { EventManager.RegisterClassHandler(typeof(TouchButton), PreviewTouchEvent, new RoutedEventHandler(TouchButton_PreviewTouch), true); EventManager.RegisterClassHandler(typeof(TouchButton), TouchEvent, new RoutedEventHandler(TouchButton_Touch), true); } private static void TouchButton_PreviewTouch(object sender, RoutedEventArgs e) { MessageBox.Show("Class TouchButton_PreviewTouch"); } private static void TouchButton_Touch(object sender, RoutedEventArgs e) { MessageBox.Show("Class TouchButton_Touch"); } public static RoutedEvent TouchEvent = EventManager.RegisterRoutedEvent("Touch", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(TouchButton)); public event RoutedEventHandler Touch { add { AddHandler(TouchEvent, value); } remove { RemoveHandler(TouchEvent, value); } } public static RoutedEvent PreviewTouchEvent = EventManager.RegisterRoutedEvent( "PreviewTouch", RoutingStrategy.Tunnel, typeof(RoutedEventHandler), typeof(TouchButton)); public event RoutedEventHandler PreviewTouch { add { AddHandler(PreviewTouchEvent, value); } remove { RemoveHandler(PreviewTouchEvent, value); } } protected override void OnClick() { RaiseTouchEvent(); } private void RaiseTouchEvent() { RoutedEventArgs touchEventArgs = new RoutedEventArgs(PreviewTouchEvent); RaiseEvent(touchEventArgs); if (!touchEventArgs.Handled) RaiseEvent(new RoutedEventArgs(TouchEvent)); } } </code></pre> <p>Here are the instance handlers in the window code behind:</p> <pre><code>private void TouchButton_PreviewTouch(object sender, RoutedEventArgs e) { MessageBox.Show(string.Format("{0} Instance PreviewTouch", ((FrameworkElement)sender).Name)); } private void TouchButton_Touch(object sender, RoutedEventArgs e) { MessageBox.Show(string.Format("{0} Instance Touch", ((FrameworkElement)sender).Name)); } </code></pre> <p>Here is the control XAML:</p> <pre><code>&lt;Grid Name="Grid" Controls:TouchButton.PreviewTouch="TouchButton_PreviewTouch"&gt; &lt;Controls:TouchButton x:Name="TouchButton" Width="200" Height="45" FontSize="24" Content="Touch me" Touch="TouchButton_Touch" PreviewTouch="TouchButton_PreviewTouch" /&gt; &lt;/Grid&gt; </code></pre> <p>I do understand that the tunneling event is handled by the <code>Grid</code> element before 'tunneling' down to the <code>TouchButton</code> element, but I thought that the class handlers were always supposed to fire before the instance handlers. If not, how can I achieve this?</p> <p><strong>UPDATE >>></strong></p> <p>Thanks to @sanguine's answer, I managed to find a way to stop all instance handlers from handling the event. If instead of replacing the declared class handling type of <code>TouchButton</code> with <code>Grid</code> as sanguine suggested, I replace it with <code>FrameworkElement</code>, then it will catch all <code>FrameworkElement</code>-derived controls.</p> <pre><code>EventManager.RegisterClassHandler(typeof(FrameworkElement), PreviewTouchEvent, new RoutedEventHandler(TouchButton_PreviewTouch), true); </code></pre>
 

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