如何实现MDI窗体不重复打开同一个子窗体？

01     FormChild formChild = new FormChild();//实例化FormChild子窗体
02     bool isOpened = false;//定义子窗体打开标记，默认值为false
03     foreach (Form form in this.MdiChildren)//循环MDI中的所有子窗体
04     {
05         if (formChild.Name == form.Name)//若该子窗体已被打开
06         {
07             formChild.Activate();//激活该窗体
08             formChild.StartPosition = FormStartPosition.CenterParent;
09             formChild.WindowState = FormWindowState.Normal;
10             isOpened = true;//设置子窗体的打开标记为true
11             formChild.Dispose();//销毁formChild实例
12             break;
13         }
14     }
15     if (!isOpened)//若该子窗体未打开，则显示该子窗体
16     {
17         formChild.MdiParent = this;
18         formChild.Show();
19     }