C#WinForm中如何判断鼠标是否在某个控件以外按下

先定义一个全局变量public Point p = new Point();
private void Form1_MouseMove(object sender, MouseEventArgs e)
{
p = e.Location;
}
private void Form1_MouseUp(object sender, MouseEventArgs e)
{
if (!this.groupBox1.ClientRectangle.Contains(p))
{
MessageBox.Show("在groupBox1外面");
}

}
之后还得把其它所有控件都加上MouseUp事件，里面都写
if (!this.groupBox1.ClientRectangle.Contains(p))
{
MessageBox.Show("在groupBox1外面");
}

private static int count = 0; //统计点击次数
自己写的事件
public void Sum_Click(object sender, EventArgs e)
{
count = count + 1;
}
Button的OnClick事件
protected void lbtnTextBox_Click(object sender, EventArgs e)
{
count = count + 1;
Response.Write("<script>alert('被点击次数为"+count+&quo