C# MDI中，关闭窗体时怎么判断关闭的是父窗体还是子窗体

if (e.CloseReason == CloseReason.MdiFormClosing)//判断点击的是父窗体还是子窗体
{ }
else if (e.CloseReason == CloseReason.UserClosing)
{
e.Cancel = true;
MessageBox.Show(“无法进行关闭”);
}