Handled RoutedEvent continues to bubble up tree

Question

I'm developing a TreeView based control and my double click event continues to bubble up my TreeViewItem nodes.

The goal is to have the TreeViewItem expand or collapse when it is double clicked.

I have a style that applies an event handler for the MouseDoubleClick event to each TreeViewItem.

Here's the code that handles the event

private void TreeViewItemDoubleClicked( object sender, RoutedEventArgs e )
{
    // Get the specific tree view item that was double clicked
    TreeViewItem treeViewItem = sender as TreeViewItem;

    // not null?
    if( null != treeViewItem )
    {
         // Switch expanded state
         if( true == treeViewItem.IsExpanded )
         {
             treeViewItem.IsExpanded = false;
         }
         else
         {
             treeViewItem.IsExpanded = true;
         }

         // Set event handled
         e.Handled = true; // [1]
    }
}

This works fine for the top level TreeViewItem however when a child is double clicked, the event bubbles up the tree causing the entire branch to collapse. Why is the event continuing to bubble? As noted a [1] I'm setting the event as handled.

Comptroller

Answer 1

Hate answering my own questions but here is the solution that I ultimately came to use.

After coming across a few sources that specified that the MouseDoubleClick is raised for each TreeViewItem in the branch ( from child up to the root ) regardless if the event is handled I utilized the answer from this question:

WPF TreeView, get TreeViewItem in PreviewMouseDown event

to get the TreeViewItem that was under the mouse event. If the current sender is equal to the TreeViewItem of the mouse event I expand/collapse as required. Otherwise, I just ignore the event and do nothing.

Comptroller

Answer 2

No idea why, but the selected answer didn't work for every TreeViewItems for me. So I used a simple bool approach to fence from reeintering TreeViewItemDoubleClicked more than once.

private void TreeViewItemDoubleClicked( object sender, RoutedEventArgs e )
{
    // Make sure the event has never been handled first
    if (bubblingBulkwark)
        return;

    // Get the specific tree view item that was double clicked
    TreeViewItem treeViewItem = sender as TreeViewItem;

    // not null?
    if( null != treeViewItem )
    {
         // Switch expanded state
         if( true == treeViewItem.IsExpanded )
         {
             treeViewItem.IsExpanded = false;
         }
         else
         {
             treeViewItem.IsExpanded = true;
         }

         // Raise bulkwark
         bubblingBulkwark = true;
    }
}

To allow the very first handler invoked to execute fully (therefore relying on the fact that a child's handler will be called before it's parent's), simply add :

private void TreeView_PreviewMouseDown(object sender, MouseButtonEventArgs e)
{
    bubblingBulkwark = false;
}

And don't forget to register it.

treeView.PreviewMouseDown += TreeView_PreviewMouseDown;

Billyebilobate