Form1 implementation：
procedure TForm1.N11Click(Sender: TObject);//點選按鈕(mainmenu元件)
begin
  if not Assigned(Form2) then
    Form2 := TForm2.Create(Self);
  Form2.Show;
end;
    

Form2 implementation：
procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := CaFree;
end;
procedure TForm2.FormDestroy(Sender: TObject);
begin
  Form2 := nil;
end;