Windows.Forms DragLeave事件意外触发

Question

自定义UserControl ChartControlShelf包含一个TableLayoutPanel，其中包含3个子控件，所有类型都为Panel。孩子们没有EventHandlers。

ShelfContainer为UserControl添加所有EventHandler ChartControlShelf：

ChartControlShelf chartControlShelf = new ChartControlShelf();
chartControlShelf.DragOver+=new DragEventHandler(chartControlShelf_DragOver);
chartControlShelf.DragLeave+=new EventHandler(chartControlShelf_DragLeave); 

...

private void chartControlShelf_DragOver(object sender, DragEventArgs e) {

        ChartControlShelf chartControlShelf = (ChartControlShelf)sender;

        if (chartControlShelf.panelControlShelf.PointToClient(Cursor.Position).Y < chartControlShelf.tlpChartControlShelf.Size.Height / 2) {
            chartControlShelf.panelInsertTop.BackColor = CustomColorsColors.DragEnter;
            chartControlShelf.panelInsertBottom.BackColor = CustomColorsColors.DragLeave;
        }
        else {
            chartControlShelf.panelInsertBottom.BackColor = CustomColorsColors.DragEnter;
            chartControlShelf.panelInsertTop.BackColor = CustomColorsColors.DragLeave;
        }
   }

    private void chartControlShelf_DragLeave(object sender, EventArgs e) {
        ChartControlShelf chartControlShelf = (ChartControlShelf)sender;
        chartControlShelf.panelInsertTop.BackColor = CustomColorsColors.DragLeave;
        chartControlShelf.panelInsertBottom.BackColor = CustomColorsColors.DragLeave;

    }

为什么* chartControlShelf_DragLeave *在鼠标离开ChartControlShelf UserControl之前触发？

Answer 1

鼠标光标“属于”指针下方直接可见的控件。听起来很奇怪，当光标“进入”ChartControlShelf中的一个控件时，它也“离开”ChartControlSelf。