modal view 上显示 navigation bar

向下实例显示modeview时不会显示上方的navigation bar

ModalViewController *modal = [[ModalViewController alloc] init];
[self presentModalViewController:model animated:YES];
[modal release];

需要这么实用才可以

ModalViewController *modal = [[ModalViewController alloc] init];
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:modal];
[self presentModalViewController:nav animated:YES];
[modal release];