C# TreeView树节点上下移动

/// <summary>
       /// 上移
       /// </summary>
       /// <param name="sender"></param>
       /// <param name="e"></param>
       private void tsbMoveUp_Click(object sender, EventArgs e)
       {
           if (Tv_tree.SelectedNode == null)
           {
               MessageBox.Show("请选择需要移动的的节点！");
               this.Focus();
               return;
           }
           folder  model = new folder();
           TreeNode node = Tv_tree.SelectedNode;     //获得选中节点的值
           model.folderId = node.Tag.ToString();
           model.TheOrder = node.Name.ToString();
           if (node.PrevNode == null)      //选中节点的上一个节点为Null则返回
           {
               return;
           }
           folder upModel = new folder();
           TreeNode upNode = node.PrevNode;            //获得选中节点的上一个节点
           upModel.folderId = upNode.Tag.ToString();
           upModel.TheOrder = upNode.Name;
           bool flag = folderOperation.MoveUp(model, upModel);       //将两个节点的排序编号互换
           if (flag)       //如果执行成功
           {
               string theOrder = node.Name;
               node.Name = upNode.Name;
               upNode.Name = theOrder;
               TreeNode newNode = (TreeNode)node.Clone();      //克隆选中的节点
               if (node.Parent == null)
               {
                   Tv_tree.Nodes.Insert(upNode.Index, newNode);      //在选中节点的上一个节点的地方插入本节点
               }
               else
               {
                   node.Parent.Nodes.Insert(upNode.Index, newNode);
               }
               node.Remove();
               Tv_tree.SelectedNode = newNode;
           }
           else
           {
               return;
           }
       }
       /// <summary>
       /// 下移
       /// </summary>
       /// <param name="sender"></param>
       /// <param name="e"></param>
       private void tsbMoveDown_Click(object sender, EventArgs e)
       {
           if (Tv_tree.SelectedNode == null)
           {
              MessageBox.Show("请选择需要移动的的节点！");
               this.Focus();
               return;
           }
           folder model = new folder();
           TreeNode node = Tv_tree.SelectedNode;     //选中的节点
           model.folderId = node.Tag.ToString();
           model.TheOrder = node.Name.ToString();
           if (node.NextNode == null)      //下一个节点为Null时返回
           {
               return;
           }
           folder downModel = new folder();
           TreeNode dowNode = node.NextNode;
           downModel.folderId = dowNode.Tag.ToString();
           downModel.TheOrder = dowNode.Name;
           bool flag = folderOperation.MoveUp(model, downModel);
           if (flag)
           {
               string theOrder = node.Name;
               node.Name = dowNode.Name;
               dowNode.Name = theOrder;
               TreeNode newNode = (TreeNode)dowNode.Clone();       //克隆下一个节点及其所有的子节点
               if (node.Parent == null)
               {
                   Tv_tree.Nodes.Insert(node.Index, newNode);    //在原节点的位置插入下一个节点的值
               }
               else
               {
                   node.Parent.Nodes.Insert(node.Index, newNode);
               }
               dowNode.Remove();           //删除掉选中节点的下一个节点
               Tv_tree.SelectedNode = node;  //重新选中
           }
           else
           {
               return;
           }
       }

string sql = string.Format("update folder set theorder = '{0}' where folderid = '{1}'", model.TheOrder, upModel.folderId);
string sql1 = string.Format("update folder set theorder = '{0}' where folderid = '{1}'", upModel.TheOrder, model.folderId);

     /// <summary>
        /// 节点的展开和折叠
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void tvDocInfo_AfterExpand(object sender, TreeViewEventArgs e)
        {
            if (e.Node.Parent == null)
            {
                TreeView tree = (TreeView)sender;
                tree.AfterCheck -= new TreeViewEventHandler(this.tvDocInfo_AfterExpand);
                //折叠其他同级节点
                TreeNode parentNode = e.Node.Parent;
                if (parentNode != null)
                {
                    foreach (TreeNode tn in parentNode.Nodes)
                    {
                        if (tn != e.Node)
                            tn.Collapse();
                    }
                }
                else
                {
                    foreach (TreeNode tn in tree.Nodes)
                    {
                        if (tn != e.Node)
                            tn.Collapse();
                    }
                }
            }

        }

节点拖拽，必须设置TreeView的AllowDrop属性为True;

private Point Position = new Point(0, 0);

private void treeView1_ItemDrag(object sender, ItemDragEventArgs e)
{
    DoDragDrop(e.Item, DragDropEffects.Move);
}

private void treeView1_DragEnter(object sender, DragEventArgs e)
{
    if (e.Data.GetDataPresent(typeof(TreeNode)))
        e.Effect = DragDropEffects.Move;
    else
        e.Effect = DragDropEffects.None;
}

private void treeView1_DragDrop(object sender, DragEventArgs e)
{
    TreeNode myNode = null;
    if (e.Data.GetDataPresent(typeof(TreeNode)))
    {
        myNode = (TreeNode)(e.Data.GetData(typeof(TreeNode)));
    }
    else
    {
        MessageBox.Show("error");
    }
    Position.X = e.X;
    Position.Y = e.Y;
    Position = tvType.PointToClient(Position);
    TreeNode DropNode = this.tvType.GetNodeAt(Position);
    if (FunctionsUI.CreateQuestionDialog("是否要将"+myNode.Text+"移动"+DropNode.Text+"类别下？") == DialogResult.OK)
    {
        // 1.目标节点不是空。2.目标节点不是被拖拽接点的字节点。3.目标节点不是被拖拽节点本身
        if (DropNode != null && DropNode.Parent != myNode && DropNode != myNode)
        {
            TreeNode DragNode = myNode;
            // 将被拖拽节点从原来位置删除。
            myNode.Remove();
            // 在目标节点下增加被拖拽节点
            DropNode.Nodes.Add(DragNode);
        }
        // 如果目标节点不存在，即拖拽的位置不存在节点，那么就将被拖拽节点放在根节点之下
        if (DropNode == null)
        {
            TreeNode DragNode = myNode;
            myNode.Remove();
            tvType.Nodes.Add(DragNode);
        }
    }
}