Silverlight Tip 7#: Handling ListBox MouseLeftButtonDown event with VisualTreeHelper

In Silverlight 2 beta 2 ListBoxItem (and ListBox) doesn’t trigger MouseLeftButtonDown event anymore! You can add handler for this event in XAML of ItemContainerStyle. I wrote post about it 9 days ago.

If you wouldn't specify the event handler in XAML, you have a problem: you can't modify code of ListBoxItem class. But you can use visual tree after loading ListBox.

You can examine the visual tree structure with VisualTreeHelper class. I have written recursive method to get all visual elements which parents are objects of a specific type:

private static List<UIElement> children = new List<UIElement>();
   
...

private static void GetChildrenWithParentRec(UIElement parent, Type targetType)
{
    int count = VisualTreeHelper.GetChildrenCount(parent);
    if (count > 0)
    {
        for (int i = 0; i < count; i++)
        {
            UIElement child = (UIElement)VisualTreeHelper.GetChild(parent, i);
            if (VisualTreeHelper.GetParent(child).GetType() == targetType)
            {
                children.Add(child);
            }
            GetChildrenWithParentRec(child, targetType);
        }
    }
}

I have used this method to obtain visuals which are children of ListBoxItem elements of ListBox control. Before you show ListBox, you can use code:

//GetChildrenWithParent uses GetChildrenWithParentRec
List<UIElement> children = ChildrenHelper.GetChildrenWithParent(listBox, typeof(ListBoxItem));            

if (children.Count > 0){
    foreach (UIElement el in children)
        el.MouseLeftButtonDown += new MouseButtonEventHandler(ListBoxItem_MouseLeftButtonDown);
}    

It works for me.