iOS自定义转场动画无法用presentingViewControll（fromView）中的view问题

iOS自定义转场动画无法用presentingViewControll（fromView）中的view问题

问题描述

• 最近自己实现一个淘宝购物车动画效果（控制器A modal 一个控制器B，A的控制器view后移并实现一个动画效果，b控制器展现一部分），发现无法改变控制器A的view

效果图

                ————>      

• 动画播放器中Animator中主要代码如下(ps:modalPresentationStyle为custom)

  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
      static int flag = 0;    //flag 确定是点击购物车，还是返回
      flag++;
  
      UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
      UIView *destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];
  
      if (flag % 2) { //动画效果处理
          [[transitionContext containerView] addSubview:destinationView];
  
          CATransform3D transform = CATransform3DIdentity;
          transform.m34 = -0.001;
          transform = CATransform3DRotate(transform,  M_PI_4 * .2, 1, 0, 0);
          transform = CATransform3DTranslate(transform, 0, 0, -100);
  
          [UIView animateWithDuration:[self transitionDuration:nil] * 0.5 animations:^{
              fromView.layer.transform = transform;
          } completion:^(BOOL finished) {
              [UIView animateWithDuration:[self transitionDuration:nil] * 0.5 animations:^{
                  fromView.layer.transform = CATransform3DMakeScale(.9, .9, 1);
              } completion:nil];
          }];
  
          destinationView.frame = [UIScreen mainScreen].bounds;
          destinationView.transform = CGAffineTransformTranslate(destinationView.transform, 0, kScreenBounsSize.height - 400);
          [UIView animateWithDuration:[self transitionDuration:nil] animations:^{
              destinationView.transform = CGAffineTransformIdentity;
          } completion:^(BOOL finished) {
              [transitionContext completeTransition:YES];
          }];
  
      }else{
          [UIView animateWithDuration:[self transitionDuration:nil] animations:^{
              fromView.transform = CGAffineTransformTranslate(fromView.transform, 0, kScreenBounsSize.height - 400);
              destinationView.layer.transform = CATransform3DIdentity;
          } completion:^(BOOL finished) {
              [transitionContext completeTransition:YES];
          }];
      }
  }   
  

解决办法

• 将fromView 和 destinationView直接从控制器调用

• 即将

   UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
   UIView *destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];
  

  改为

  UIView *fromView = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey].view;
  UIView *destinationView = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey].view;
  

原因

• 我们将代码改为UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];和UIView *destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];打印发现fromView出现了null：

  2017-02-22 11:33:49.254 taobaoEffect[1376:323552] fromView ----- (null)
  2017-02-22 11:33:49.255 taobaoEffect[1376:323552] destinationView ----- <UIView: 0x7fb433c03690; frame = (0 0; 414 736); autoresize = W+H; gestureRecognizers = <NSArray: 0x60000005e540>; layer = <CALayer: 0x60000002e0c0>>
  

• 这里似乎没有任何问题，看文档也没有任何解释。但这又是一个Apple的一个坑，这在默认的文档下是没有的，但如果你下载文档了以后再看，你会发现在viewForKey:方法中会有这么解释(Apple提醒你文档的重要性again) viewForKey: may return nil which would indicate that the animator should not manipulate the associated view controller’s view. 当viewController的view不该被animator所操作时，将返回nil

  // Currently only two keys are defined by the system -
  // UITransitionContextFromViewKey, and UITransitionContextToViewKey
  // viewForKey: may return nil which would indicate that the animator should not
  // manipulate the associated view controller's view.
  - (nullable __kindof UIView *)viewForKey:(UITransitionContextViewKey)key NS_AVAILABLE_IOS(8_0);
  

具体代码

https://github.com/NewYorkFive/taobaoShopListAnimator_Demo/tree/master