WPF Treeview Recursive Expand/Collapse

The following class contains an expansion method that allows for dynamic expansion and collapse of a WPF (untested with Silverlight, might work as well) TreeView. The second method parameter provides a way to define the depth of expansion/collapse.

public static class TreeViewExt
{
    /// <summary>
    /// Expands/collapses a treeview control recursively. Since for a hierarchical data template, the items will
    /// only be generated when displayed - and only then can be expanded, the method attaches an event to the 
    /// StatusChanged event of the ItemsContainerGenerator and waits until they are in fact generated to recursively
    /// call the expand method on these items.
    /// </summary>
    /// 
    /// <param name="itemsControl"> ItemsControl, can be treeview or treeviewitem </param>
    /// <param name="expand"> expand = false collapses, expand = true expands </param>
    /// <param name="levelDepth"> for levelDepth = int.MaxValue, the entire tree will be expanded/collapsed.  
    /// For any  other value n of levelDepth, only n levels away from the supplied itemsControl will be expanded
    /// or collapsed to. </param>
    public static void ExpandRecursively(this ItemsControl itemsControl, bool expand, int levelDepth)
    {
        // decrease level depth for next recursive call only if levelDepth != int.MaxValue
        int depth = levelDepth == int.MaxValue ? levelDepth : levelDepth - 1;
 
        // expand the item
        TreeViewItem treeViewItem = itemsControl as TreeViewItem;
        if (treeViewItem != null)
            treeViewItem.IsExpanded = expand || levelDepth >= 0; // expand, or keep expanded when levelDepth >= 0
 
        // continue if levelDepth is still bigger than 0, or if subitems need to be collapsed
        if (levelDepth > 0 || !expand)
        {
            // get container generator of itemsControl
            ItemContainerGenerator itemContainerGenerator = itemsControl.ItemContainerGenerator;
 
            // if containers have already been generated, the subItems can be expanded/collapsed
            if (itemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
            {
                for (int i = itemsControl.Items.Count - 1; i >= 0; --i)
                {
                    ItemsControl childControl = itemContainerGenerator.ContainerFromIndex(i) as ItemsControl;
                    if (childControl != null)
                        childControl.ExpandRecursively(expand, depth);
                }
            }
            // otherwise, we have to wait for the containers to be generated. attach event to listen for status
            else
            {
                EventHandler handler = null; // store in variable, so the handler can be detached
                handler = new EventHandler((s, e) =>
                {
                    if (itemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
                    {
                        for (int i = itemsControl.Items.Count - 1; i >= 0; --i)
                        {
                            ItemsControl childControl = itemContainerGenerator.ContainerFromIndex(i) as ItemsControl;
                            if (childControl != null)
                                childControl.ExpandRecursively(expand, depth);
                            itemContainerGenerator.StatusChanged -= handler; // detach
                        }
                    }
                });
                itemContainerGenerator.StatusChanged += handler; // attach
            }
        }
    }
}