RoutedEvent Tunnel does not reach child

Question

I found a lot of example explaining bubbling but none about Tunneling this is about Tunneling eg parent to child. I think my main problem is that i don't understand how to register the routed event in the child (WindowControl to UserControl). I got:

public partial class MyParent : UserControl
{
  public static readonly RoutedEvent RoutedMouseUpEvent = EventManager.RegisterRoutedEvent(
        "PreviewMouseLeftButtonUp", RoutingStrategy.Tunnel, typeof(RoutedEventHandler),   typeof(WindowControl)); 

// Provide CLR accessors for the event        
public event RoutedEventHandler MouseUp
{
  add { AddHandler(RoutedMouseUpEvent, value); }
  remove { RemoveHandler(RoutedMouseUpEvent, value); }
}

public addView(UserControl view)
{
WindowControl win = new WindowControl();
win.Content = view;
}

private void Grid_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
  RoutedEventArgs newEventArgs = new RoutedEventArgs(MyParent.RoutedMouseUpEvent);
            RaiseEvent(newEventArgs);
}
}

The encapsulation of addView is necessary, should be no problem? The child is added via addView. Grid_MouseLeftButtonUp is called.
The receiver looks like this (It is mvvm so there isn't much):

public partial class ChildView : UserControl
{
 void UserControl_PreviewMouseLeftButtonUp(object sender, RoutedEventArgs args)
 {
    int i = 0; // The breakpoint is never called
 }
}

in the xaml

<Grid>
   <Border BorderBrush="black" BorderThickness="1" HorizontalAlignment="Center"   VerticalAlignment="Center" PreviewMouseLeftButtonUp="UserControl_PreviewMouseLeftButtonUp">
</Border>
</Grid>

If I forgot something please let me know. The problem is, that the routed event does not reach UserControl_PreviewMouseLeftButtonUp

Adi Lester · Accepted Answer · 2012-11-20T14:46:38.617

11

This is not how tunneling routing strategy works. Tunneling means that the event will start from the root and go down the tree path to the calling control. For example if we have the following visual tree

Window
|
|--> SomeUserControl
|--> MyParent
     |
     |--> ChildView

then if MyParent will raise a tunneling event, the tunneling event will visit:

Window
MyParent

and NOT

MyParent
ChildView

So to summarize, bubbling events will always start at the control raising the event and stop at the root of the visual tree, while tunneling events will start at the root of the visual tree and end at the control raising the event (exact same path, only reverse order).

EDIT: You can read more about routed events in MSDN's Routed Events Overview. It also has a nice image demonstrating this:

enter image description here

edited Nov 20 '12 at 14:46

answered Nov 20 '12 at 14:37

Adi Lester

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I don't understand. Why can't I just tell the programm that MyParent is the root? – Martin Nov 20 '12 at 14:39
2

Now I understand. Tunneling can not reach my child, which makes it quite useless in my opinion. I did read those docks but somehow didn't understand it this way. I will solve my problem using Interfaces and simply passing data (this was plan B). Thank you for excelent explaination. – Martin Nov 20 '12 at 14:59
1

Tunneling is not useless, it's simply used for a different task than the one you're attempting. For example, it could be used to disallow typing certain characters in a TextBox by capturing key presses and canceling the event before it reaches the TextBox. – Adi Lester Nov 20 '12 at 15:06

RoutedEvent Tunnel does not reach child

1 Answers1