向上，向下，向左和向右箭头键不会触发KeyDown事件

    protected override bool IsInputKey(Keys keyData)    {        switch (keyData)        { case Keys.Right: case Keys.Left: case Keys.Up: case Keys.Down:     return true; case Keys.Shift | Keys.Right: case Keys.Shift | Keys.Left: case Keys.Shift | Keys.Up: case Keys.Shift | Keys.Down:     return true;        }        return base.IsInputKey(keyData);    }    protected override void onKeyDown(KeyEventArgs e)    {        base.onKeyDown(e);        switch (e.KeyCode)        { case Keys.Left: case Keys.Right: case Keys.Up: case Keys.Down:     if (e.Shift)     {     }     else     {     }     break;  }    }