winform 点击按钮，弹出窗体，弹出窗体的位置在按钮的下方

private void button_Click(object sender, EventArgs e)
{
    Button btn = (Button)sender; //点击的按钮
    Form form = new Form(this);//弹出的窗体
    form.StartPosition = FormStartPosition.Manual;//必须要设置这一步
    form.Location = btn.PointToScreen(new Point(0, btn.Height));//使用PointToScreen()方法进行坐标设置
    form.Show();
}