-(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event{    //切换方法1    //动画效果：左右滑动    //必须有导航器视图才能切换    [self.navigationController pushViewController:[[ViewController2 alloc]init] animated:YES];        //切换方法2：    //动画效果：从下滑动到上遮盖住之前的视图,如果有导航栏也被遮盖住了    ViewController2 *controller = [[ViewController2 alloc]init];    [self presentViewController:controller animated:YES completion:NULL];        //切换方法3：    //动画效果：上下的翻动，上下左右的转动，保留导航栏    //必须都是子视图    ViewController2 *controller1 = [[ViewController2 alloc]init];    ViewController2 *controller2 = [[ViewController2 alloc]init];    [self addChildViewController:controller1];    [self.view addSubview:controller1.view];    [self addChildViewController:controller2];    [self.view addSubview:controller2.view];                [self transitionFromViewController:controller1                      toViewController:controller2                              duration:1                               options:UIViewAnimationOptionTransitionCurlDown                            animations:^{}                            completion:^(BOOL finished) {}];}