(1)在Form1的implementation底下打上：
   uses Unit2;
(2)procedure TForm1.Button1Click(Sender: TObject);
   begin
     if not Assigned(Form2) then//判斷是否已開啟
       Application.CreateForm(TForm2, Form2);
     Form2.Show;
   end;
(3)procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction);
   begin
     Action := CaFree;
   end;
(4)procedure TForm2.FormDestroy(Sender: TObject);
   begin
     Form2 := nil;
   end;