WPF中关于自定义控件的滚动条鼠标停留在内容上鼠标滚轮滚动无效的问题

//在构造函数中绑定treeview的鼠标滚轮事件，原因是在xmal前台绑定时触发不了MouseWheel事件
public TreeViewList()
        {
            InitializeComponent();
            treeview.AddHandler(TreeView.MouseWheelEvent, new MouseWheelEventHandler(treeview_MouseWheel), true);
        }

//根据父控件对象查找指定类型的子控件
private T GetVisualChild<T>(DependencyObject parent) where T : Visual
        {
            T child = default(T);
            int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
            for (int i = 0; i < numVisuals; i++)
            {
                Visual v = (Visual)VisualTreeHelper.GetChild(parent, i);
                child = v as T;
                if (child == null)
                {
                    child = GetVisualChild<T>(v);
                }
                if (child != null)
                {
                    break;
                }
            }
            return child;
        }

private void treeview_MouseWheel(object sender, MouseWheelEventArgs e)
        {
            //在treeview的基础上，层层查找，直到找到它的父容器，是个NavToolbar（滚动条是NavToolbar的滚动条，并非treeview的）
            try
            {
                var scroll =
                GetVisualChild<ScrollViewer>(
                    ((((((((treeview.Parent as Grid).Parent as ChapterList).Parent as Grid).Parent as ScrollViewer).
                            Parent as Border).Parent as Grid).Parent as Grid).Parent as Border).Parent);
                if (scroll != null)
                {
                    scroll.ScrollToVerticalOffset(scroll.VerticalOffset - e.Delta);
                }
            }
            catch (Exception)
            {
            }
        }