iOS：探究视图控制器的转场动画

一、介绍

在iOS开发中，转场动画的使用无处不见，不只是我们自己更多的使用UIViewblock动画实现一个转场动画，其实，在我们实现VC控制器跳转的时候都是转场动画的实现，例如标签栏控制器的切换、模态动画present和dismiss、导航控制器的push和pop。实现它们的转场动画，只需要实现它们的动画协议即可，说起来有点太笼统，不如看下面的图吧：

二、分析

对于上面的三种类型的控制器，系统都会为它们设置一个代理，通过这个代理方法去监测它们切换VC的过程，这个过程仅仅是出现和消失的过程，至于这个过程是什么过渡效果，这个代理是不管的。要想这个过程是有动画的，那么在这些过程中，也就是代理函数中，需要另外再返回一个实现动画的对象，这个对象必须遵循实现动画的协议，在这个协议中开发者可以重写自定义转场动画。下面会慢慢演示这三种类型控制器的自定义转场动画。

重写不可交互转场动画的核心协议内容：

//重写动画协议
@protocol UIViewControllerAnimatedTransitioning <NSObject>

//动画执行时间
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;

//自定义动画效果
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@end

重写可交互转场动画的核心协议内容：

//重写动画协议
@protocol UIViewControllerInteractiveTransitioning <NSObject>

//自定义动画效果
- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@end

系统提供的一个百分比可交互转场动画核心类内容：

//系统提供的百分比动画类，已经遵循了可交互协议
@interface UIPercentDrivenInteractiveTransition : NSObject <UIViewControllerInteractiveTransitioning>
- (void)pauseInteractiveTransition;
- (void)updateInteractiveTransition:(CGFloat)percentComplete;
- (void)cancelInteractiveTransition;
- (void)finishInteractiveTransition;

@end

三、转场动画View之间的切换

四、实现一个自定义的模态动画

1、概述

正如我们所知，系统为我们提供的模态动画默认是从底部present出，然后dismiss回到底部。 虽然说这个基本能够满足使用，但是如果我们还想使用其他形式的模态动画例如从顶部present出dismiss回到顶部，这个时候就需要对系统默认的转场动画进行自定义了。

2、详解

（1）要自定义模态转场动画，首先需要给被模态的控制器设置一个实现了UIViewControllerAnimatedTransitioning协议的代理，这些协议方法可以监测动画执行的过程，代理和协议如下：

//代理
@protocol UIViewControllerTransitioningDelegate;
@interface UIViewController(UIViewControllerTransitioning)
@property (nullable, nonatomic, weak) id <UIViewControllerTransitioningDelegate> transitioningDelegate API_AVAILABLE(ios(7.0));
@end

//协议
@protocol UIViewControllerTransitioningDelegate <NSObject>
@optional
//present时调用，返回一个实现了不可交互转场动画协议的代理
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

//dismiss时调用，返回一个实现了不可交互转场动画协议的代理
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed;

//presnt过程中交互时调用，返回一个实现了可交互的转场动画协议的代理
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

//dismiss过程中交互时调用，返回一个实现了可交互的转场动画协议的代理
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

//返回新的模态弹框控制器（这个是对模态风格进行自定义时调用，后面会说到）
- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(nullable UIViewController *)presenting sourceViewController:(UIViewController *)source API_AVAILABLE(ios(8.0));
@end

（2）然后在上面的协议方法中返回一个实现了UIViewControllerAnimatedTransitioning协议的代理，在这个代理的协议方法中可以真正重写转场动画了，协议如下：

@protocol UIViewControllerAnimatedTransitioning <NSObject>
//动画执行时间
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
//自定义转场动画
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
@optional

（3）自定义转场动画实现如下【注意：Singleton单例类和UIView+Extesion分类需要自己去拷贝引入】

• 设置UIViewControllerAnimatedTransitioning代理对象TransitionDelegate，监测动画执行过程，将其设置为单例

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  @interface TransitionDelegate : NSObject<UIViewControllerTransitioningDelegate>
  SingletonH(TransitionDelegate);
  @end

  #import "TransitionDelegate.h"
  #import "CustomAnimationTransition.h"
  
  @implementation TransitionDelegate
  SingletonM(TransitionDelegate);
  
  #pragma mark - <UIViewControllerTransitioningDelegate>
  
  //展示的动画
  - (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
  {
      CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
      animation.presented = YES;
      return animation;
  }
  
  //关闭的动画
  - (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
  {
      CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
      animation.presented = NO;
      return animation;
  }
  @end

• 设置UIViewControllerAnimatedTransitioning代理对象CustomTransitionAnimationTransition，重写动画效果

  #import <UIKit/UIKit.h>
  
  @interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
  //判断是present还是dismiss, YES:present  NO:dismisss
  @property (assign,nonatomic)BOOL presented;
  @end

• //设置过渡动画（modal和dismiss的动画都需要在这里处理）
  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      // UITransitionContextToViewKey,
      // UITransitionContextFromViewKey.
  
      //出来的动画
      if (self.presented) {
  
          //获取并添加转场视图
          UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
          [transitionContext.containerView addSubview:toView];
  
          //设置动画从上往下出来
          toView.y = -toView.height;
  
          [UIView animateWithDuration:duration animations:^{
  
              toView.y = ;
  
          } completion:^(BOOL finished) {
  
              //移除视图
              BOOL cancle = [transitionContext transitionWasCancelled];
              if (cancle) {
                  [toView removeFromSuperview];
              }
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:!cancle];
          }];
      }
      //销毁的动画
      else
      {
          //获取转场视图
          UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
  
          [UIView animateWithDuration:duration animations:^{
  
              fromView.y = -fromView.height;
  
          } completion:^(BOOL finished) {
  
              //移除视图
              BOOL cancle = [transitionContext transitionWasCancelled];
              if (!cancle) {
                  [fromView removeFromSuperview];
              }
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:!cancle];
          }];
      }
  }

• 开始执行，结果如gif图 

  //present
  UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
  nav.transitioningDelegate = [TransitionDelegate sharedTransitionDelegate];//自定义转场动画
  nav.modalPresentationStyle = UIModalPresentationFullScreen;
  [self presentViewController:nav animated:YES completion:nil];

• 

（4）我们已经实现了一个简单的自定义模态不可交互的转场动画，其实，在模态控制器的时候，我们还可以自定义可交互的转场动画以及设置自定义的模态风格。可交互的转场动画一会儿再讨论，先来讨论一下模态风格，系统在iOS13之前默认都是满屏模式的UIModalPresentationFullScreen，但是iOS13之后，默认是UIModalPresentationPageSheet。系统提供的模态风格如下：

//模态风格枚举
typedef NS_ENUM(NSInteger, UIModalPresentationStyle) {
    UIModalPresentationFullScreen = ,
    UIModalPresentationPageSheet ,
    UIModalPresentationFormSheet ,
    UIModalPresentationCurrentContext ,
    UIModalPresentationCustom , //自定义
    UIModalPresentationOverFullScreen ,
    UIModalPresentationOverCurrentContext ),
    UIModalPresentationPopover ,
    UIModalPresentationBlurOverFullScreen ,
    UIModalPresentationNone,
    UIModalPresentationAutomatic ,
};

（5）从上面的枚举可以看到，系统是支持我们实现自己的风格的，也就是自定义。在实现自定义之前，一定得知道UIPresentationController这个类，这个是弹出框控件，模态的控制器都是由它进行管理，主要代码如下：

//重写此方法可以在弹框即将显示时执行所需要的操作
- (void)presentationTransitionWillBegin;
//重写此方法可以在弹框显示完毕时执行所需要的操作
- (void)presentationTransitionDidEnd:(BOOL)completed;
//重写此方法可以在弹框即将消失时执行所需要的操作
- (void)dismissalTransitionWillBegin;
//重写此方法可以在弹框消失之后执行所需要的操作
- (void)dismissalTransitionDidEnd:(BOOL)completed;
//重写决定了弹出框的frame
- (CGRect)frameOfPresentedViewInContainerView;
//重写对containerView进行布局
- (void)containerViewWillLayoutSubviews;
- (void)containerViewDidLayoutSubviews;
//初始化方法
- (instancetype)initWithPresentedViewController:(UIViewController *)presentedViewController presentingViewController:(UIViewController *)presentingViewController;

（6）额外再提一个知识点，因为一会儿在自定义模态风格时会涉及到。在本文开篇结构图中介绍了创建的转场动画都是在转场动画上下文UIViewControllerContextTransitioning协议中完成的，那么这个转场动画的执行是谁管理呢？看结构图如下，没错，是由UIViewControllerTransitionCoordinator这个代理协调器在协调器上下文中完成的，系统给UIViewController提供了一个分类，这个分类持有这个代理协调器，通过这个代理协调器可以拿到执行转场动画的方法。最终，我们可以自己添加一些操作与转场动画同步执行。

UIViewControllerContextTransitioning协议核心内容

@protocol UIViewControllerTransitionCoordinatorContext <NSObject>
// 执行的属性
@property(nonatomic, readonly, getter=isAnimated) BOOL animated;
@property(nonatomic, readonly) UIModalPresentationStyle presentationStyle;
@property(nonatomic, readonly) NSTimeInterval transitionDuration;
@property(nonatomic, readonly) UIView *containerView;
@property(nonatomic, readonly) CGAffineTransform targetTransform 

// 参与控制器
// UITransitionContextToViewControllerKey、UITransitionContextFromViewControllerKey
- (nullable __kindof UIViewController *)viewControllerForKey:(UITransitionContextViewControllerKey)key;

// 参与的视图
// UITransitionContextToViewKey、UITransitionContextFromViewKey
- (nullable __kindof UIView *)viewForKey:(UITransitionContextViewKey)key API_AVAILABLE(ios(8.0));
@end

UIViewControllerTransitionCoordinator协议核心内容

// 与动画控制器中的转场动画同步，执行其他动画
- (BOOL)animateAlongsideTransition:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))animation
                        completion:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))completion;

// 与动画控制器中的转场动画同步，在指定的视图内执行动画
- (BOOL)animateAlongsideTransitionInView:(nullable UIView *)view
                               animation:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))animation
                              completion:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))completion;

UIViewController(UIViewControllerTransitionCoordinator) 分类核心内容

//持有转场动画执行协调器
@interface UIViewController(UIViewControllerTransitionCoordinator)
@property(nonatomic, readonly, nullable) id <UIViewControllerTransitionCoordinator> transitionCoordinator;
@end

（7）自定义模态风格实现如下【注意：Singleton单例类和UIView+Extesion分类需要自己去拷贝引入】

• 设置UIViewControllerAnimatedTransitioning代理对象TransitionDelegate，监测动画执行过程并返回模态风格，将其设置为单例

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  
  @interface TransitionDelegate : NSObject<UIViewControllerTransitioningDelegate>
  SingletonH(TransitionDelegate);
  @end

  #import "TransitionDelegate.h"
  #import "CustomPresentationController.h"
  #import "CustomAnimationTransition.h"
  
  @implementation TransitionDelegate
  SingletonM(TransitionDelegate);
  
  #pragma mark - <UIViewControllerTransitioningDelegate>
  //返回模态风格
  -(UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(UIViewController *)presenting sourceViewController:(UIViewController *)source
  {
      return [[CustomPresentationController alloc] initWithPresentedViewController:presented presentingViewController:presenting];
  }
  
  //展示的动画
  - (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
  {
      CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
      animation.presented = YES;
      return animation;
  }
  
  //关闭的动画
  - (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
  {
      CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
      animation.presented = NO;
      return animation;
  }
  @end

• 设置UIViewControllerAnimatedTransitioning代理对象CustomTransitionAnimationTransition，重写动画效果

  #import <UIKit/UIKit.h>
  
  @interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
  //判断是present还是dismiss, YES:present  NO:dismisss
  @property (assign,nonatomic)BOOL presented;
  @end

  #import "CustomAnimationTransition.h"
  #import "UIView+Extension.h"
  
  const CGFloat duration = 0.5f;
  
  @implementation CustomAnimationTransition
  
  #pragma mark -<UIViewControllerAnimatedTransitioning>
  //动画时间
  - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      return duration;
  }
  
  //设置过渡动画（modal和dismiss的动画都需要在这里处理）
  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      // UITransitionContextToViewKey,
      // UITransitionContextFromViewKey.
      
  　　 //发现此处并没有添加toView到containerView中以及从containerView中移除toView，与上面的有区别。
      //我把添加和移除toView的操作放到了下面的自定义的模态风格类中完成的
  
      //出来的动画
      if (self.presented) {
           UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
  
          //设置动画从上往下出来
          toView.y = -toView.height;
  
          [UIView animateWithDuration:duration animations:^{
  
              toView.y = ;
  
          } completion:^(BOOL finished) {
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:YES];
          }];
      }
      //销毁的动画
      else
      {
          [UIView animateWithDuration:duration animations:^{
  
              UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
  
              fromView.y = -fromView.height;
  
          } completion:^(BOOL finished) {
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:YES];
          }];
      }
  }

• 设置自定义的模态风格类CustomPresenttationController

  #import "CustomPresentationController.h"
  
  @implementation CustomPresentationController
  
  //可以改变被模态的控制器视图的尺寸
  - (CGRect)frameOfPresentedViewInContainerView
  {
  　　 //CGRectInset: 在containerView的frame基础上，将width减小100，将height减小200
      //containerView是容纳presentedView的一个容器
      return CGRectInset(self.containerView.bounds, , );
  }
  
  //将上面重置的frame完成布局
  - (void)containerViewDidLayoutSubviews {
      self.presentedView.frame = self.frameOfPresentedViewInContainerView;
      [super containerViewDidLayoutSubviews];
  }
  
  //过渡即将展示时的处理
  //这个过程可以改变视图属性、或者添加视图等
  - (void)presentationTransitionWillBegin
  {
      self.presentedView.frame = self.containerView.frame;
      [self.containerView addSubview:self.presentedView];
  }
  
  //过渡展示完成
  //做清理工作
  - (void)presentationTransitionDidEnd:(BOOL)completed
  {
       if (!completed) {
          [self.presentedView removeFromSuperview];
       }
  }
  
  //过渡即将消失时的处理
  //这个过程可以改变视图属性等
  - (void)dismissalTransitionWillBegin
  {
      //例如改变透明度，与转场控制器中的转场动画同步执行
      [self.presentingViewController.transitionCoordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
  
          self.presentedView.alpha = .f;
  
      } completion:nil];
  }
  
  //过渡消失完成
  //做清理工作
  - (void)dismissalTransitionDidEnd:(BOOL)completed
  {
      if (completed) {
          [self.presentedView removeFromSuperview];
      }
  }
  @end

• 开始执行，结果如gif图

  //present
  UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
  nav.transitioningDelegate = [TransitionDelegate sharedTransitionDelegate];//自定义转场动画
  nav.modalPresentationStyle = UIModalPresentationCustom; //自定义模态风格
  [self presentViewController:nav animated:YES completion:nil];

  

（8）自定义模态转场动画和自定义模态风格我们都实现完了，但是上面的动画过程中都是不可交互的，那么要想实现可交互的动画该怎么做呢？如上面所说的，在dismiss时返回一个实现了UIViewControllerInteractiveTransitioning协议的代理或者直接是原生类UIPercentDrivenInteractiveTransition对象。其中，UIPercentDrivenInteractiveTransition是系统封装好了百分比驱动，用起来很简单，那么真正的实现原理还是我们去实现一下。下面咱们来实现导航模式的交互效果，如下：

• TransitioningDelegate

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  
  @interface TransitioningDelegate : NSObject<UIViewControllerTransitioningDelegate>
  SingletonH(TransitioningDelegate);
  @end

  #import "TransitioningDelegate.h"
  #import "CustomAnimationTransition.h"
  #import "CustomInteractiveTransition.h"
  
  @implementation TransitioningDelegate
  SingletonM(TransitioningDelegate);
  
  #pragma mark - UIViewControllerTransitioningDelegate
  
  //present
  - (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
  
       //这里还是采用自定义的转场动画方式进行present，使其present时从屏幕右侧滑入
       CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
       animation.presented = YES;
       return animation;
  }
  
  //dismiss,必须重写
  - (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
      //这里采用自定义的转场动画覆盖系统的dismiss效果，在dismiss时，由于自定义了交互动画，所以系统自己的dismiss动画不会执行
      CustomAnimationTransition *animation = [[CustomAnimationTransition alloc] init];
      animation.presented = NO;
      return animation;
  }
  
  //将要dismiss时的交互行为，必须重写
  - (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator {
  
      CustomInteractiveTransition *animation = [[CustomInteractiveTransition alloc] init];
      return animation;
  }
  
  @end

• CustomAnimationTransition

  #import <UIKit/UIKit.h>
  
  @interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
  //判断是present还是dismiss, YES:present  NO:dismisss
  @property (assign,nonatomic)BOOL presented;
  @end

  #import "CustomAnimationTransition.h"
  #import "UIView+Extension.h"
  
  const CGFloat duration = 0.5f;
  
  @implementation CustomAnimationTransition
  
  #pragma mark -<UIViewControllerAnimatedTransitioning>
  //动画时间
  - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      return duration;
  }
  
  //设置过渡动画（modal和dismiss的动画都需要在这里处理）
  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      // UITransitionContextToViewKey,
      // UITransitionContextFromViewKey.
  
      //出来的动画
      if (self.presented) {
  
          //获取并添加转场视图
          UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
          [transitionContext.containerView addSubview:toView];
  
          //设置动画从右往左出来
          toView.x = toView.width;
  
          [UIView animateWithDuration:duration animations:^{
  
              toView.x = ;
  
          } completion:^(BOOL finished) {
  
              //移除视图
              BOOL cancle = [transitionContext transitionWasCancelled];
              if (cancle) {
                  [toView removeFromSuperview];
              }
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:!cancle];
          }];
      }
      //销毁的动画
      else
      {
          //不做处理，而是交给自定义的交互动画去完成
      }
  }
  @end

• CustomInteractiveTransition

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  
  @interface CustomInteractiveTransition : NSObject<UIViewControllerInteractiveTransitioning>
  SingletonH(CustomInteractiveTransition); //采用单例的方式主要是为了保存交互上下文
  
  //动画进度更新
  -(void)updateAnimationProgress:(CGFloat)progress;
  
  //动画完成
  -(void)finish;
  
  //动画取消
  -(void)cancel;
  
  @end

  #import "CustomInteractiveTransition.h"
  #import "UIView+Extension.h"
  
  @interface CustomInteractiveTransition ()
  @property (nonatomic, strong) id<UIViewControllerContextTransitioning> context;
  @end
  
  @implementation CustomInteractiveTransition
  SingletonM(CustomInteractiveTransition);
  
  #pragma mark - UIViewControllerInteractiveTransitioning
  
  //开始交互时调用
  - (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
  
      //保存上下文
      self.context = transitionContext;
  
      //更改视图层级
      UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
      UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
      [transitionContext.containerView insertSubview:toView belowSubview:fromView];
  }
  
  //动画进度更新
  -(void)updateAnimationProgress:(CGFloat)progress {
  
      UIView *fromView = [self.context viewForKey:UITransitionContextFromViewKey];
      fromView.x = self.context.containerView.width * progress;
  
  }
  
  //动画完成
  -(void)finish {
      
      UIView *fromView = [self.context viewForKey:UITransitionContextFromViewKey];
      [UIView animateWithDuration:0.2 animations:^{
  
          fromView.x += self.context.containerView.width;
  
      } completion:^(BOOL finished) { 
          [fromView removeFromSuperView]; 
          [self.context completeTransition:finished];
      }];
  }
  
  //动画取消
  -(void)cancel {
      
      UIView *fromView = [self.context viewForKey:UITransitionContextFromViewKey];
      [UIView animateWithDuration:0.2 animations:^{
  
          fromView.x = ;
  
      } completion:^(BOOL finished) {
         [fromView removeFromSuperView]; 
         [self.context cancelInteractiveTransition];
      }];
  }
  @end

• 在被模态的控制器添加拖拽手势

  #import "SecondViewController.h"
  #import "CustomInteractiveTransition.h"
  
  @interface SecondViewController ()
  
  @end
  
  @implementation SecondViewController
  
  - (void)viewDidLoad {
      [super viewDidLoad];
  
      self.title = @"secondVc";
      self.view.backgroundColor = [UIColor redColor];
  
      [self.view addGestureRecognizer:[[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)]];
  }
  
  -(void)pan:(UIPanGestureRecognizer *)pan {
  
      CGPoint translatedPoint = [pan translationInView:self.view];
      CGFloat progress = translatedPoint.x / [UIScreen mainScreen].bounds.size.width;
      if (progress < ) {
          return;
      }
      //拖拽的距离进度比
      progress = fabs(progress);
      CustomInteractiveTransition *transition = [[CustomInteractiveTransition alloc] init];
      switch (pan.state) {
          case UIGestureRecognizerStateBegan:
              [self dismissViewControllerAnimated:YES completion:nil];
              break;
          case UIGestureRecognizerStateChanged:
              [transition updateAnimationProgress:progress];
              break;
          case UIGestureRecognizerStateEnded:
          {
              if (progress > 0.5) {
                  [transition finish];
              }else{
                  [transition cancel];
              }
              break;
          }
          default:
              break;
      }
  }
  @end

• 开始执行，结果如gif图

  UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
  nav.transitioningDelegate = [TransitioningDelegate sharedTransitioningDelegate];//自定义可交互转场动画
  nav.modalPresentationStyle = UIModalPresentationFullScreen; //系统模态风格
  [self presentViewController:nav animated:YES completion:nil];  

五、实现一个自定义的导航动画

1、重写导航控制器的协议，返回自定义的导航转场动画，动画实现的方式和modal思想一致，重写的核心协议如下：

//重写导航控制器协议
@protocol UINavigationControllerDelegate <NSObject>
@optional
................

//返回一个实现了自定义交互动画的对象
- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController;

//返回一个实现了普通动画的对象
- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC;
@end

2、 现在就来自定义一个导航转场动画，步骤如下：

• 创建一个CustomNavigationTransition类，实现导航控制器的协议

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  
  NS_ASSUME_NONNULL_BEGIN
  
  @interface CustomNavigationTransition : NSObject<UINavigationControllerDelegate>
  SingletonH(CustomNavigationTransition);
  @end
  
  NS_ASSUME_NONNULL_END

  #import "CustomNavigationTransition.h"
  #import "CustomNavigationAnimation.h"
  
  @implementation CustomNavigationTransition
  SingletonM(CustomNavigationTransition);
  
  #pragma mark - UINavigationControllerDelegate
  
  //返回一个实现了普通动画的对象
  - (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                     animationControllerForOperation:(UINavigationControllerOperation)operation
                                                  fromViewController:(UIViewController *)fromVC
                                                             toViewController:(UIViewController *)toVC {
  
      CustomNavigationAnimation *animation = [[CustomNavigationAnimation alloc] init];
      animation.operation = operation;
      return animation;
  }
  
  @end

• 自定义一个CustomNavigationAnimation类，实现动画协议，重写动画效果

  #import <UIKit/UIKit.h>
  
  NS_ASSUME_NONNULL_BEGIN
  
  @interface CustomNavigationAnimation : NSObject<UIViewControllerAnimatedTransitioning>
  @property (nonatomic, assign) UINavigationControllerOperation operation;
  @end
  
  NS_ASSUME_NONNULL_END

  #import "CustomNavigationAnimation.h"
  #import "UIView+Extension.h"
  
  const CGFloat _duration = 0.5f;
  
  @implementation CustomNavigationAnimation
  
  #pragma mark -<UIViewControllerAnimatedTransitioning>
  //动画时间
  - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      return _duration;
  }
  
  //设置过渡动画（modal和dismiss的动画都需要在这里处理）
  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      // UITransitionContextToViewKey,
      // UITransitionContextFromViewKey.
  
      //push
      if (self.operation == UINavigationControllerOperationPush) {
  
          //转场视图
          UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
          [transitionContext.containerView addSubview:toView];
  
          //设置动画从右上push进来
          toView.x = toView.width;
          toView.y = -toView.height;
  
          [UIView animateWithDuration:_duration animations:^{
  
              toView.x = ;
              toView.y = ;
  
          } completion:^(BOOL finished) {
  
              //移除视图
              BOOL cancle = [transitionContext transitionWasCancelled];
              if (cancle) {
                  [toView removeFromSuperview];
              }
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:!cancle];
          }];
      }
      //pop
      else if(self.operation == UINavigationControllerOperationPop)
      {
          //转场视图，更改层级关系
          UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
          UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
          [transitionContext.containerView insertSubview:toView belowSubview:fromView];
  
          [UIView animateWithDuration:_duration animations:^{
  
              //pop返回右上
              fromView.x = fromView.width;
              fromView.y = -fromView.height;
  
          } completion:^(BOOL finished) {
  
              //移除视图
              BOOL cancle = [transitionContext transitionWasCancelled];
              if (!cancle) {
                  [fromView removeFromSuperview];
              }
  
              //动画完成后,视图上的事件才能处理
              [transitionContext completeTransition:!cancle];
          }];
      }
  }
  @end

• 开始执行，结果如gif图

  //push
  ThirdViewController *vc = [[ThirdViewController alloc] init];
  self.navigationController.delegate = [CustomNavigationTransition sharedCustomNavigationTransition];
  [self.navigationController pushViewController:vc animated:YES];

  

六、实现一个自定义的标签栏切换动画

1、重写标签栏控制器的协议，返回自定义的标签栏切换转场动画，动画实现的方式和modal思想一致，重写的核心协议如下：

//重写标签栏协议
@protocol UITabBarControllerDelegate <NSObject>
@optional
......................

//返回一个实现了可交互的标签栏转场动画对象
- (nullable id <UIViewControllerInteractiveTransitioning>)tabBarController:(UITabBarController *)tabBarController
                      interactionControllerForAnimationController: (id <UIViewControllerAnimatedTransitioning>)animationController;

//返回一个实现了普通的标签栏转场动画对象
- (nullable id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
            animationControllerForTransitionFromViewController:(UIViewController *)fromVC
                                              toViewController:(UIViewController *)toVC;

@end

2、 现在就来自定义一个标签转场动画，步骤如下：

• 创建一个CustomTabBarViewController类，设置代理CustomTabbarTransition实例

  //注意：我使用StoryBoard搭建的界面
  #import <UIKit/UIKit.h>
  NS_ASSUME_NONNULL_BEGIN
  @interface CustomTabBarViewController : UITabBarController
  @end
  NS_ASSUME_NONNULL_END

  #import "CustomTabBarViewController.h"
  #import "CustomTabbarTransition.h"
  
  @interface CustomTabBarViewController ()
  
  @end
  
  @implementation CustomTabBarViewController
  
  -(instancetype)initWithCoder:(NSCoder *)coder {
      if (self = [super initWithCoder:coder]) {
          //设置代理
          self.delegate = [CustomTabbarTransition sharedCustomTabbarTransition];
      }
      return self;
  }
  
  - (void)viewDidLoad {
      [super viewDidLoad];
  
  }
  @end

• 创建一个CustomTabbarTransition类，实现标签栏控制器的协议

  #import <UIKit/UIKit.h>
  #import "Singleton.h"
  
  NS_ASSUME_NONNULL_BEGIN
  
  @interface CustomTabbarTransition : NSObject<UITabBarControllerDelegate>
  SingletonH(CustomTabbarTransition);
  @end
  
  NS_ASSUME_NONNULL_END

  #import "CustomTabbarTransition.h"
  #import "CustomTabbarAnimation.h"
  
  @implementation CustomTabbarTransition
  SingletonM(CustomTabbarTransition);
  
  #pragma mark - UITabBarControllerDelegate
  //返回一个实现了普通动画的对象
  - (nullable id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
  animationControllerForTransitionFromViewController:(UIViewController *)fromVC
                                                         toViewController:(UIViewController *)toVC {
  
      CustomTabbarAnimation *animation = [[CustomTabbarAnimation alloc] init];
      return animation;
  }
  
  @end

• 创建一个CustomTabbarAnimation类，自定义标签切换动画

  #import <UIKit/UIKit.h>
  
  NS_ASSUME_NONNULL_BEGIN
  
  @interface CustomTabbarAnimation : NSObject<UIViewControllerAnimatedTransitioning>
  
  @end
  
  NS_ASSUME_NONNULL_END

  #import "CustomTabbarAnimation.h"
  #import "UIView+Extension.h"
  
  const CGFloat _Duration = 0.5f;
  
  @implementation CustomTabbarAnimation
  
  #pragma mark -<UIViewControllerAnimatedTransitioning>
  //动画时间
  - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      return _Duration;
  }
  
  //设置过渡动画（modal和dismiss的动画都需要在这里处理）
  - (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
  {
      // UITransitionContextToViewKey,
      // UITransitionContextFromViewKey.
  
      //转场视图
      UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
      UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
      [transitionContext.containerView addSubview:toView];
      [transitionContext.containerView sendSubviewToBack:toView];
  
      //尺寸变化,从原尺寸缩小到点
      CGRect finalFrame = CGRectInset(transitionContext.containerView.frame, transitionContext.containerView.frame.size.width/, transitionContext.containerView.frame.size.height/);
  
      [UIView animateWithDuration:_Duration animations:^{
  
                  fromView.frame = finalFrame;
  
             } completion:^(BOOL finished) {
  
                 //移除视图
                 BOOL cancle = [transitionContext transitionWasCancelled];
                 if (!cancle) {
                     [fromView removeFromSuperview];
                 }
  
                 //动画完成后,视图上的事件才能处理
                 [transitionContext completeTransition:!cancle];
             }];
  }
  @end

• 开始执行，结果如gif图

七、总结

好了，这三种常用的转场动画都进行了自定义，当然至于后两种的交互转场动画跟modal实现原理一样，就不介绍了。借用和修改别人的一个图，做个总结吧，如下：