publicpartialclassForm1:Form { publicForm1() { InitializeComponent(); } Form2f; privatevoidbutton1_Click(objectsender,EventArgse) { if(f==null)//如果子窗體為空則創造例項並顯示 { f=newForm2(); f.StartPosition=FormStartPosition.CenterScreen;//子窗體居中顯示 f.Show(); } else { if(f.IsDisposed)//若子窗體關閉則開啟新子窗體並顯示 { f=newForm2(); f.StartPosition=FormStartPosition.CenterScreen;//子窗體居中顯示 f.Show(); } else{ f.Activate();//使子窗體獲得焦點 } } }}