拖拽TreeView节点

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

private void treeView1_DragEnter(object sender, DragEventArgs e)
{
    e.Effect = DragDropEffects.Move;
}

private void treeView1_DragDrop(object sender, DragEventArgs e)
{
    Point targetPoint = treeView1.PointToClient(new Point(e.X, e.Y));
    TreeNode targetNode = treeView1.GetNodeAt(targetPoint);
    TreeNode draggedNode = (TreeNode)e.Data.GetData(typeof(TreeNode));
    if (draggedNode == null)
    {
        return;
    }
    if (targetNode == null)
    {
        draggedNode.Remove();
        treeView1.Nodes.Insert(targetNode.Index, draggedNode);
    }
    else
    {
        TreeNode parentNode = targetNode;
        if (!draggedNode.Equals(targetNode) && targetNode != null)
        {
            bool canDrop = true;
            while (canDrop && (parentNode != null))
            {
                canDrop = !Object.ReferenceEquals(draggedNode, parentNode);
                parentNode = parentNode.Parent;
            }
            if (canDrop)
            {
                TreeNode treeNode = draggedNode.Parent;
                int index = draggedNode.Index;
                if (index < targetNode.Index)
                {
                    return;
                }
                draggedNode.Remove();
                treeNode.Nodes.Insert(targetNode.Index, draggedNode);
                targetNode.Remove();
                treeNode.Nodes.Insert(index, targetNode);
            }
        }
    }
    treeView1.SelectedNode = draggedNode;
}

private void Form1_Load(object sender, EventArgs e)
{
    treeView1.AllowDrop = true;
}

测试结果：