private childItem FindVisualChild<childItem>(DependencyObject obj)
            where childItem : DependencyObject
        {
            for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
            {
                DependencyObject child = VisualTreeHelper.GetChild(obj, i);
                if (child != null && child is childItem)
                    return (childItem)child;
                else
                {
                    childItem childOfChild = FindVisualChild<childItem>(child);
                    if (childOfChild != null)
                        return childOfChild;
                }
            }
            return null;
        }