iOS自定義轉場動畫無法用presentingViewControll（fromView）中的view問題

問題描述

• 最近自己實作一個淘寶購物車動畫效果（控制器A modal 一個控制器B，A的控制器view後移并實作一個動畫效果，b控制器展現一部分），發現無法改變控制器A的view

效果圖

      ————>      

• 動畫播放器中Animator中主要代碼如下(ps:modalPresentationStyle為custom)

  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
      static int flag = 0;    //flag 确定是點選購物車，還是傳回
      flag++;
  
      UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
      UIView *destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];
  
      if (flag % 2) { //動畫效果處理
          [[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];
          }];
      }
  }   
             

解決辦法

• 将

  fromView

  和

  destinationView

  直接從控制器調用
• 即将

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

  改為

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

原因

• 我們将代碼改為

  UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];

  和

  UIView *destinationView = [transitionContext viewForKey:UITransitionContextToViewKey];

  列印發現

  fromView

  出現了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>>
             

• 這裡似乎沒有任何問題，看文檔也沒有任何解釋。但這又是一個Apple的一個坑，這在預設的文檔下是沒有的，但如果你下載下傳文檔了以後再看，你會發現在

  viewForKey:

  方法中會有這麼解釋(Apple提醒你文檔的重要性again) viewForKey: may return nil which would indicate that the animator should not manipulate the associated view controller’s view. 當viewController的view不該被animator所操作時，将傳回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);
             

具體代碼

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