项目中的一个树形结节，既要响应拖拽事件、又要响应点击事件。实现的时候没多想，依次实现了tree_MouseClick、tree_MouseDown、tree_MouseMove事件。出现的Bug是，偶尔会点击时不响应。

分析下来，应该是触发了MouseMove里的DoDragDrop拖拽事件，因此MouseClick被忽略了。如何正确实现呢？这个帖子里给出了精确的解释，摘录如下：

Good implemented D'n'D doesn't start the operation on mouse down.

The drag operation has to start if the user presses the mouse button and

moves the mouse on a certain distance from the button-down point. Only if

this happens and all other conditions are met (see Bob's post) the

operation should be considered as starting D'n'D.

SystemInformation class has a property DragSize that should be used for

the size of the rectangle arround the click point in which the drag

operation shouldn't start.

大意就是说，不能一MouseMove就触发拖拽，而要超出一定距离之后，再触发。超出的范围，可以用系统设置SystemInformation.DragSize。于是在MouseMove里添加判断：

1 private void tree_MouseMove(object sender, MouseEventArgs e) 2 { 3     if (mouseDownPosition == Point.Empty || 4         Math.Abs(e.X - mouseDownPosition.X) <= SystemInformation.DragSize.Width || 5         Math.Abs(e.Y - mouseDownPosition.Y) <= SystemInformation.DragSize.Height) 6     { 7         return; 8     } 9     (sender as TreeList).DoDragDrop(data, DragDropEffects.Copy);10 }

搞定。