//第一种方式
procedure TForm1.btn1Click(Sender: TObject);
begin
With TForm2.Create(Application) do
Try
   ShowModal;
finally
   free;
end;
end;
 
//第二种方式
procedure TForm1.btn2Click(Sender: TObject);
begin
  if not assigned(Form2) then
  begin
    Form2:=TForm2.Create(nil);
    Form2.Show;
  end
end;
 
//第二种方式创建的的窗体需要在FORM2里释放资源
procedure TForm2.FormClose(Sender: TObject; var Action: TCloseAction);
begin
   Form2:=nil;           //Form对象指向空地址
  Action := cafree;     //Form关闭后释放占用的内存
end;