Why do items in TreeViewItem inherit the event handlers of parent?

Question

So, I create a TreeViewItem (parentNode), and I add TreeViewItems into the parentNode TreeViewItem. I then add a MouseButtonEventHandler to the parentNode, and now all the TreeViewItems inside parentNode have the MouseButtonEventHandler. I've run the debugger to see if I have code that was accidentally written to add the MouseButtonHandler, but there isn't...

Edit: I did additional tests, and it even goes two levels down. Is there a way to isolate eventhandlers to only the specific node and not its children and/or parents?

public newClass() {
    TreeViewItem parent = new TreeViewItem();

    TreeViewItem childOne = new TreeviewItem();
    addExpandClickListener(childOne);

    TreeViewItem childTwo = new TreeviewItem();
    TreeViewItem childThree = new TreeViewItem();


    childTwo.Items.Add(childThree);
    childOne.Items.Add(childTwo);
    parent.Items.Add(childOne);
    TreeViewObject.Items.Add(parent);
}

private void addExpandClickListener(TreeViewItem item) { item.MouseLeftButtonUp += new MouseButtonEventHandler(item_MouseClick); }


private void item_MouseClick(object sender, MouseButtonEventArgs e) {
    // Define click event as handled
    e.Handled = true;
    if(sender != e.Source) return;
    // Handle click event
    TreeViewItem root = (TreeViewItem)sender;
    if(root.IsExpanded == true) CollapseRecursive(root);
    else root.IsExpanded = true;
    //else root.ExpandSubtree();
    ViewTree.Items.Refresh();
}

Answer 1

The area of the parentNode includes the areas of the children. Think of overlapping rectangles. If you only want to have a click to work for the text part, you'll either have to supply your own DataTemplate or use the visual tree to find the header and apply the click to that.