13.自定义过渡效果

主要分为 自定义视图控制器过渡（时间的函数） 和 交互式视图控制器过渡（手势）。

所有的过渡，都会创建一个过渡协调器。

将UICollectionViewController集合视图控制器的useLayoutToLayoutNavigationTransitions属性设置为YES，在将集合视图推入导航控制器之前，推入过渡会使用 setCollectionViewLayout:animated: 来完成集合视图布局的变化。

iOS 7中可以 取消交互式导航控制器过渡，那么要注意可能出现的问题，第一个控制器的ViewWillDisappear，但不会调用ViewDidAppear和ViewDidDisappear。第二个控制器的ViewWillAppear会调用，但ViewDidAppear不会被调用。无论过渡成功或失败都可以通过notifyWhenInteractionChanges收到通知

自定义视图控制器过渡

// 给跳转的控制器的过渡效果设置代理
dest.transitioningDelegate = self;

// 实现 UIViewControllerTransitioningDelegate 协议方法
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
  return 1.0f;
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
  // 获得将要消失或出现的视图控制器的指针，可以设置透明度、frame的改变等实现一些动画效果
  UIViewController *src = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  UIViewController *dest = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
}

// 负责返回动画对象
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
  
  return self;
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
  
  return self;
}

交互式过渡动画

不需要实现animateTransition:方法，而是要实现startInteractiveTransition:方法，这个方法里只能有一个动画块。动画应该基于UIView而不是图层，交互式过渡不支持CATransition或CALayer动画。

// 一、在需要实现过渡动画的控制器内实现以下协议方法
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
  return 1.0f;
}

// 协议 <UIViewControllerInteractiveTransitioning>
- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
  
  UIViewController *src = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
  
  CGPoint centerPoint = src.view.center;
  [UIView animateWithDuration:1.0 animations:^{
    
    src.view.frame = CGRectMake(centerPoint.x, centerPoint.y, 10, 10);
    src.view.center = centerPoint;
  } completion:^(BOOL finished) {
    // 如果取消了过渡，这里要返回 NO,否则会多出一个遮挡视图 UITransitionView
    [transitionContext completeTransition:YES];
  }];
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
  
  return self;
}

- (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
  
  return self;
}

- (id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator {
  
  return self.animator; // 继承自 UIPercentDrivenInteractiveTransition
}

- (id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator {
  
  return self.animator; // UIPercentDrivenInteractiveTransition
}
  // 二、初始化过渡交互动画，并将手势与动画绑定
 self.animator = [[SCTPercentDrivenAnimator alloc] initWithViewController:self];
  UIPinchGestureRecognizer *gr = [[UIPinchGestureRecognizer alloc] initWithTarget:self.animator
                                                                           action:@selector(pinchGestureAction:)];
  
  [self.view addGestureRecognizer:gr];

// 三、过渡动画类的实现
@interface SCTPercentDrivenAnimator (/*Private Methods*/)
@property (nonatomic, assign) float startScale;
@property (weak, nonatomic) UIViewController *controller;
@end

@implementation SCTPercentDrivenAnimator

-(instancetype) initWithViewController:(UIViewController*) controller {
  if((self = [super init])) {
    self.controller = controller;
  }
  return self;
}

-(void) pinchGestureAction:(UIPinchGestureRecognizer*) gestureRecognizer {
  
  CGFloat scale = gestureRecognizer.scale;
  if(gestureRecognizer.state == UIGestureRecognizerStateBegan) {
    
    self.startScale = scale;
    [self.controller dismissViewControllerAnimated:YES completion:nil];
  }
  if(gestureRecognizer.state == UIGestureRecognizerStateChanged) {
    
    CGFloat completePercent = 1.0 - (scale/self.startScale);
    [self updateInteractiveTransition:completePercent];
  }
  if(gestureRecognizer.state == UIGestureRecognizerStateEnded) {
    
    if(gestureRecognizer.velocity >= 0)
       [self cancelInteractiveTransition];
    else
      [self finishInteractiveTransition];
  }
  
  if(gestureRecognizer.state == UIGestureRecognizerStateCancelled) {
    
    [self cancelInteractiveTransition];
  }
}
@end