预览
1.接受协议
@interface FirstViewController : UIViewController <UIViewControllerTransitioningDelegate>
2.设置transitioningDelegate
SecondViewController *secView = [[SecondViewController alloc] init];
secView.transitioningDelegate = self;
[self presentViewController:secView animated:YES completion:nil];
3.实现animationControllerForDismissedController方法，返回一个SACCollapseAnimator对象，可自定义过场时间和碎片大小
- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
SACCollapseAnimator *animator = [[SACCollapseAnimator alloc] init];
//animator.duration = 1;
//animator.sideLength = 8;
return animator;
}