C# WinForms - 在同一 TreeViewControl 中拖放

Question

我正在尝试在同一控件中实现树视图项的 DragDrop。

我希望能够将一个项目从一个节点移动到另一个节点。

这是我当前的代码，当我运行它时，我可以看到项目已开始拖动，但窗口图标不允许将其拖放到控件上的任何节点。

我当前的代码

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)
{
    if (e.Data.GetDataPresent(typeof(TreeNode)))
    {
        TreeNode sourceNode = e.Data.GetData(typeof(TreeView)) as TreeNode;

        var item = new TreeNode(sourceNode.Text);


        System.Drawing.Point pt = ((TreeView)sender).PointToClient(new System.Drawing.Point(e.X, e.Y));
        TreeNode DestinationNode = ((TreeView)sender).GetNodeAt(pt);

        DestinationNode.Nodes.Add(item);
        DestinationNode.Expand();
    }
}

Answer 1

只需将treeView1_DragDrop函数修改为：

private void treeView1_DragDrop(object sender, DragEventArgs e)
{
    // Retrieve the client coordinates of the drop location.
    Point targetPoint = treeView1.PointToClient(new Point(e.X, e.Y));

    // Retrieve the node at the drop location.
    TreeNode targetNode = treeView1.GetNodeAt(targetPoint);

    // Retrieve the node that was dragged.
    TreeNode draggedNode = (TreeNode)e.Data.GetData(typeof(TreeNode));

    // Confirm that the node at the drop location is not 
    // the dragged node and that target node isn't null
    // (for example if you drag outside the control)
    if (!draggedNode.Equals(targetNode) && targetNode != null)
    {
        // Remove the node from its current 
        // location and add it to the node at the drop location.
        draggedNode.Remove();
        targetNode.Nodes.Add(draggedNode);

        // Expand the node at the location 
        // to show the dropped node.
        targetNode.Expand();
    }
}

Answer 2

在树控件上设置AllowDrop=true。

Answer 3

略微改进的版本，可防止您将节点放到自身或其任何后代上

private void treeView1_DragDrop(object sender, DragEventArgs e)
{
    TreeNode draggedNode = (MatfloNode)drgevent.Data.GetData(typeof(TreeNode));

    Point pt = this.PointToClient(new System.Drawing.Point(drgevent.X, drgevent.Y));
    TreeNode targetNode = this.GetNodeAt(pt);

    TreeNode parentNode = targetNode;

    if (draggedNode != null &&
        targetNode != null  )
    {
        bool canDrop = true;
        while (canDrop && (parentNode != null))
        {
            canDrop = !Object.ReferenceEquals(draggedNode, parentNode);
            parentNode = parentNode.Parent;
        }

        if (canDrop)
        {
            draggedNode.Remove();
            targetNode.Nodes.Add(draggedNode);
            targetNode.Expand();
        }
    }
}

Answer 4

对 DragDrop 处理程序进行了一些改进和添加，以配合所有其他修订。

添加支持：

• 支持将节点拖放到树视图背景上（底部）。节点被添加到树的底部。
• 合并了 mrpurple 的“不要放在子节点上”示例并对其进行了修饰，使其与原始示例一致。
• 还这样做了，以便在拖放节点后选中它。建议在此处也加载已删除节点的内容，否则 用户可能会对当前显示的内容与选择的节点感到困惑。

注意：请务必在树视图控件上设置 AllowDrop=true，否则无法删除节点。

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)
{
    // Retrieve the client coordinates of the drop location.
    Point targetPoint = treeView1.PointToClient(new Point(e.X, e.Y));

    // Retrieve the node at the drop location.
    TreeNode targetNode = treeView1.GetNodeAt(targetPoint);

    // Retrieve the node that was dragged.
    TreeNode draggedNode = e.Data.GetData(typeof(TreeNode));

    // Sanity check
    if (draggedNode == null)
    {
        return;
    }

    // Did the user drop on a valid target node?
    if (targetNode == null)
    {
        // The user dropped the node on the treeview control instead
        // of another node so lets place the node at the bottom of the tree.
        draggedNode.Remove();
        treeView1.Nodes.Add(draggedNode);
        draggedNode.Expand();
    }
    else
    {
        TreeNode parentNode = targetNode;

        // Confirm that the node at the drop location is not 
        // the dragged node and that target node isn't null
        // (for example if you drag outside the control)
        if (!draggedNode.Equals(targetNode) && targetNode != null)
        {
            bool canDrop = true;

            // Crawl our way up from the node we dropped on to find out if
            // if the target node is our parent. 
            while (canDrop && (parentNode != null))
            {
                canDrop = !Object.ReferenceEquals(draggedNode, parentNode);
                parentNode = parentNode.Parent;
            }

            // Is this a valid drop location?
            if (canDrop)
            {
                // Yes. Move the node, expand it, and select it.
                draggedNode.Remove();
                targetNode.Nodes.Add(draggedNode);
                targetNode.Expand();
            }
        }
    }

    // Optional: Select the dropped node and navigate (however you do it)
    treeView1.SelectedNode = draggedNode;
    // NavigateToContent(draggedNode.Tag);
}