TreeView 中的 HotTracking 不适用于拖放

Question

我有一个简单的 TreeView，其 HotTracking 属性设置为 True。当我将鼠标移到某个项目上时它会起作用。但当我使用拖放并将某些内容拖到 TreeView 项上时，它不起作用。有没有办法将 HotTracking 与 DragDrop 结合使用？或者有什么解决方法吗？

Answer 1

根据设计，该控件仅获取 D+D 通知，而不获取鼠标消息。您可以简单地自己选择节点：

    private void treeView1_DragOver(object sender, DragEventArgs e) {
        if (e.Data.GetDataPresent("something")) {
            var pos = treeView1.PointToClient(new Point(e.X, e.Y));
            var hit = treeView1.HitTest(pos);
            if (hit.Location == TreeViewHitTestLocations.Label) {
                treeView1.SelectedNode = hit.Node;
                e.Effect = DragDropEffects.Copy;
            }
            else e.Effect = DragDropEffects.None;
        }
    }

您通常需要做更多工作才能让用户滚动视图并展开节点。

Answer 2

按照 @Hans 建议选择节点是一个简单的解决方案，但如果节点选择上存在一些事件，或者您只需要保留选定的节点，则可能无法使用。
我发现的唯一方法是使用 VisualStylesRenderer custumDraw 节点。

private void plTree_DragOver(object sender, DragEventArgs e)
    {            
        Point pt = plTree.PointToClient(new Point(e.X, e.Y));

        var overNode = plTree.GetNodeAt(pt);
        bool canMoveTo = overNode != null && 
                         TreeNodeIsFolder(overNode) && 
                         !IsFirstNodeParentToSecond(GetDraggedNodes(e)[0], overNode);// all dragged nodes are of the same parent
        e.Effect = canMoveTo ? DragDropEffects.Move : DragDropEffects.None;

        if (overNode == null) return;

        if (_lastCustomDrawNode != overNode)
        {
            NormalDrawNode(_lastCustomDrawNode);
            CustomDrawNode(overNode);
        }
        _lastCustomDrawNode = overNode;
    }

    private void NormalDrawNode(TreeNode aNode)
    {
        if (aNode == null) return;

        if (_normalNodeRenderer == null)
            _normalNodeRenderer = new VisualStyleRenderer("Explorer::TreeView", 1, 1);
        Debug.WriteLine("normal render" + DateTime.Now);
        RenderTreeNode(_normalNodeRenderer, aNode, true);

        _lastCustomDrawNode = null;
    }

    private void CustomDrawNode(TreeNode aNode)
    {
        if (_hotNodeRenderer == null)
            _hotNodeRenderer = new VisualStyleRenderer("Explorer::TreeView", 1, 2);
        Debug.WriteLine("custom render" + DateTime.Now);
        RenderTreeNode(_hotNodeRenderer, aNode, false);
    }

    private void RenderTreeNode(VisualStyleRenderer renderer, TreeNode aNode, bool drawDefaultBck)
    {
        if(_treeGraphics == null)
             _treeGraphics = plTree.CreateGraphics();

        const int iconShift = 21;
        Rectangle aRec = aNode.Bounds;

        var bckRec = new Rectangle(aRec.Location.X - iconShift, aRec.Location.Y, aRec.Width + iconShift, aRec.Height);

        if (!drawDefaultBck)
            renderer.DrawBackground(_treeGraphics, bckRec);
        else
            _treeGraphics.FillRectangle(_treebckgBrush, bckRec);

        var textRec = new Rectangle(aRec.Location.X + 1, aRec.Location.Y - 1, aRec.Width, aRec.Height);
        TextRenderer.DrawText(_treeGraphics, aNode.Text, GetTreeNodeFont(aNode), textRec, Color.FromKnownColor(KnownColor.ControlText));

        var imgRec = new Rectangle(aRec.Location.X + 2 - iconShift, aRec.Location.Y, 16, 16);
        renderer.DrawImage(_treeGraphics, imgRec, ImageListTree.Images[aNode.ImageIndex]);
    }

这篇文章对主题绘制有很大帮助：
VisualStyleRenderer 和主题 (WinForms)