TreeView拖动

region TreeView拖动
        private void tvFormel_ItemDrag(object sender, ItemDragEventArgs e)
        {
            TreeNode tn = e.Item as TreeNode;
            //根节点不允许拖放操作
            if ((e.Button == MouseButtons.Left) && (tn != null) && (tn.Parent != null)) 
            {
                this.tvFormel.DoDragDrop(tn, DragDropEffects.Copy | DragDropEffects.Move | DragDropEffects.Link);
            }
            //DoDragDrop(e.Item, DragDropEffects.Move);
        }

        private void tvFormel_DragEnter(object sender, DragEventArgs e)
        {
             if (e.Data.GetDataPresent("System.Windows.Forms.TreeNode"))
            {
                e.Effect = DragDropEffects.Move;
            }
            else
            {
                e.Effect = DragDropEffects.None;
            }
        }

        private void tvFormel_DragDrop(object sender, DragEventArgs e)
        {
            TreeNode NewNode;
            if (e.Data.GetDataPresent(typeof(TreeNode)))
            {
                Point pt = ((TreeView)sender).PointToClient(new Point(e.X, e.Y));

                TreeNode DestinationNode = ((TreeView)sender).GetNodeAt(pt);

                NewNode = (TreeNode)e.Data.GetData("System.Windows.Forms.TreeNode");

                DestinationNode.Nodes.Add((TreeNode)NewNode.Clone());

                DestinationNode.Expand();

                //删除已经移动的节点
                NewNode.Remove();

            }
        }
        #endregion