以下是iOS7之后，苹果开放转场动画接口结构图，分别是UITabBarControllerDelegate 、UIViewControllerTransitiningDelegate、UINavigationControllerDelegate

第一节：ViewController的模态跳转：动画自定义

UIViewControllerTransitioningDelegate
这个函数用来设置调用present方法和 dismiss 方法时，进行的转场动画

/// 执行present方法，进行的转场动画
/// presented：将要弹出的Controller
/// presenting：当前的Controller
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

/// 执行dismiss方法，进行的转场动画
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed;

/// 执行present方法，进行的交互式转场动画
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

/// 执行dismiss方法，进行的交互式转场动画
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

/// iOS8后提供的新接口  返回UIPresentationController处理转场
- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(nullable UIViewController *)presenting sourceViewController:(UIViewController *)source API_AVAILABLE(ios(8.0));

UIViewControllerAnimatedTransitioning 接口，是自定义转场动画的重点

@protocol UIViewControllerAnimatedTransitioning <NSObject>
/// 返回动画执行的时长
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
/// 自定义转场动画的实现
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
@optional

UIViewControllerContextTransitioning 接口，转场上下文，能获取到转场动画中参数及状态

@protocol UIViewControllerContextTransitioning <NSObject>
/// 容器视图： 用来表现动画
@property(nonatomic, readonly) UIView *containerView;
/// 是否应该执行动画
@property(nonatomic, readonly, getter=isAnimated) BOOL animated;
/// 是否可狡猾
@property(nonatomic, readonly, getter=isInteractive) BOOL interactive;
/// 是否被取消了
@property(nonatomic, readonly) BOOL transitionWasCancelled;
/// 转场的风格
@property(nonatomic, readonly) UIModalPresentationStyle presentationStyle;

/*
  可交互转场动画特有的
*/
/// 更新转场过程的百分比，用于可交互动画的阀值
- (void)updateInteractiveTransition:(CGFloat)percentComplete;
/// 完成可交互的转场交互动作时调用
- (void)finishInteractiveTransition;
/// 取消可交互的转场交互动作时调用
- (void)cancelInteractiveTransition;

/// 转场动画被中断、暂停时调用 
- (void)pauseInteractiveTransition API_AVAILABLE(ios(10.0));
/// 转场动画完成时调用
- (void)completeTransition:(BOOL)didComplete;


/*
  获取转场中两个视图控制器
  UITransitionContextViewControllerKey 的定义
  UITransitionContextFromViewControllerKey /// 原视图控制器
  UITransitionContextToViewControllerKey  /// 跳转的视图控制器
*/
- (nullable __kindof UIViewController *)viewControllerForKey:(UITransitionContextViewControllerKey)key;


/*
  直接获取转场中的视图
  UITransitionContextViewKey 的定义
  UITransitionContextFromViewKey  /// 原控制器的视图
  UITransitionContextToViewKey    /// 转场控制器的视图
*/
- (nullable __kindof UIView *)viewForKey:(UITransitionContextViewKey)key API_AVAILABLE(ios(8.0));

@property(nonatomic, readonly) CGAffineTransform targetTransform API_AVAILABLE(ios(8.0));

/// 获取视图控制器的初始位置
- (CGRect)initialFrameForViewController:(UIViewController *)vc;
/// 获取视图控制器转场后的位置
- (CGRect)finalFrameForViewController:(UIViewController *)vc;
@end

小案例：自定义一个从右边滑入的present转场动画

第一步：自定义转场动画，创建PanPresentAnimation实现UIViewControllerAnimatedTransitioning接口

@interface PanPresentAnimation : NSObject<UIViewControllerAnimatedTransitioning>
@end


@implementation PanPresentAnimation
/// 设置转场动画时间
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext {
    return 0.8f;
}

/// 自定义转场动画
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    /// 获取切入ViewController
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    /// 设置要切入的ViewController的初始位置
    /// 实现的效果：从右边滑入的效果
    CGRect screenBounds = [[UIScreen mainScreen] bounds];
    CGRect finalFrame = [transitionContext finalFrameForViewController:toVC];
    toVC.view.frame = CGRectOffset(finalFrame, screenBounds.size.width, 0);
    
    /// 将切入的ViewController的View添加到containerView
    UIView *containerView = [transitionContext containerView];
    [containerView addSubview:toVC.view];
    
    /// 自动定义动画：弹出动画
    NSTimeInterval duration = [self transitionDuration:transitionContext];
    [UIView animateWithDuration:duration
                          delay:0.0
         usingSpringWithDamping:0.8
          initialSpringVelocity:5
                        options:UIViewAnimationOptionCurveLinear
                     animations:^{
                         toVC.view.frame = finalFrame;
                     } completion:^(BOOL finished) {
                         /// 必须要告诉context 切换完成
                         [transitionContext completeTransition:YES];
                     }];
}
@end

第二步：遵守UIViewControllerTransitioningDelegate协议，返回自定义present转场动画PanPresentAnimation

#import "AViewController.h"
#import "BViewController.h"
#import "PanPresentAnimation"

@interface MainViewController ()<UIViewControllerTransitioningDelegate>
@end

@implementation MainViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(80.0, 210.0, 160.0, 40.0);
    [button setTitle:@"Click me" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}

-(void) buttonClicked:(id)sender {
    BViewController *mvc =  [[BViewController alloc] init];
    mvc.transitioningDelegate = self;
    mvc.modalPresentationStyle = UIModalPresentationFullScreen;
    [self presentViewController:mvc animated:YES completion:nil];
}

/// 返回自定义的present转场动画对象：BouncePresentAnimation
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
    return [PanPresentAnimation new];
}

@end

最终效果

可交互转场动画自定义

可交互转场动画，按我的理解就是可以控制转场动画的进度，比如苹果系统提供的右滑返回上一级一样。
在UIViewControllerTransitioningDelegate协议中有两个可以定义可交互转场的方法:interactionControllerForPresentation方法很少用，因为下一级界面是不确定的，常用的是interactionControllerForDismissal，因为上一级界面是确定的。

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed;

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

对于UIViewControllerTransitioningDelegate协议中对于dismiss转场动画的方法有以下两个:
一个是不可交互的普通转场：animationControllerForDismissedController
一个是可交互的转场：interactionControllerForDismissal
两者的关系苹果官方是这么写的：

（1）interactionControllerForDismissal方法中的anmatore参数是由animationControllerForDismissedController方法返回的
（2）如果interactionControllerForDismissal 返回结果是nil，则是不执行可交互动画，执行普通的转场动画（即animationControllerForDismissedController返回定义的动画）
（3）如果要执行可交互动画，那么也必须要实现animationControllerForDismissedController方法，并返回一个普通的转场动画，如果animationControllerForDismissedController返回是nil或没实现，那么interactionControllerForDismissal方法是不会执行的

小案例：在上一个案例中继续开发，在presentB界面后，自定义dismiss可交换的转场动画，效果：右滑返回。（案例：A present B，B dismiss A）

第一步：创建自定义可交换动画，PanInteractiveTransition实现UIViewControllerInteractiveTransitioning接口

@interface PanInteractiveTransition : NSObject <UIViewControllerInteractiveTransitioning>
/// 是否处于交互的状态
@property (nonatomic, assign) BOOL interacting;

/// 用于为B界面添加拖动手势
/// @param viewController BController
- (void)forPresentingViewController:(UIViewController *)viewController;
@end

@interface PanInteractiveTransition()
@property (nonatomic, strong) id<UIViewControllerContextTransitioning> context;
@property (nonatomic, strong) UIViewController *presentingViewController;
@end

@implementation PanInteractiveTransition

/// 为B界面添加拖动手势
- (void)forPresentingViewController:(UIViewController *)viewController {
    self.presentingViewController = viewController;
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(handleGesgture:)];
    [viewController.view addGestureRecognizer: pan];
}

/// 拖动手势响应
- (void)handleGesgture:(UIPanGestureRecognizer *)pan {
    CGPoint translation = [pan translationInView:pan.view.superview];
    CGFloat persent = translation.x / [UIScreen mainScreen].bounds.size.width;
    if (persent < 0) {
        return;
    }
    persent = fabs(persent);
    switch (pan.state) {
        /// 手势开始
        case UIGestureRecognizerStateBegan:
            /// 标记：交互中
            self.interacting = YES;
            /// 执行dismiss方法
            [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
            break;
        /// 拖动中
        case UIGestureRecognizerStateChanged: {
            /// 更新转场动画进度
            [self updateAniProgess:persent];
            break;
        }
        /// 拖动结束
        case UIGestureRecognizerStateEnded:
        /// 拖动取消、中断
        case UIGestureRecognizerStateCancelled: {
            /// 标记：交互结束
            self.interacting = NO;
            /// 如果滑动查过50%，则返回，否则取消返回原点
            if (persent > 0.5) {
                [self finish];
            }else{
                [self cancel];
            }
            break;
        }
        default:
            break;
    }
}

/// UIViewControllerInteractiveTransitioning协议方法
/// 触发：开始交互转场时
/// 作用：将两个ViewController中View的添加到视图容器containerView中
- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    self.context = transitionContext;
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    
    toVC.view.frame = [transitionContext finalFrameForViewController:toVC];
    [[transitionContext containerView] insertSubview:toVC.view belowSubview:fromVC.view];
}


/// 更新动画状态
- (void)updateAniProgess:(CGFloat)progress {
    UIView *frameVC = [self.context viewForKey:UITransitionContextFromViewKey];
    CGRect finalRect = CGRectMake([UIScreen mainScreen].bounds.size.width * progress, 0, frameVC.bounds.size.width, frameVC.bounds.size.height);
    frameVC.frame = finalRect;
}

/// 转场结束
- (void)finish {
    [UIView animateWithDuration:0.2 animations:^{
        UIView *frameVC = [self.context viewForKey:UITransitionContextFromViewKey];
        CGRect finalRect = CGRectMake([UIScreen mainScreen].bounds.size.width, 0, frameVC.bounds.size.width, frameVC.bounds.size.height);
        frameVC.frame = finalRect;
    } completion:^(BOOL finished) {
        [self.context completeTransition:YES];
    }];
}

/// 转场取消
- (void)cancel {
    [UIView animateWithDuration:0.2 animations:^{
        UIView *frameVC = [self.context viewForKey:UITransitionContextFromViewKey];
        CGRect finalRect = CGRectMake(0, 0, frameVC.bounds.size.width, frameVC.bounds.size.height);
        frameVC.frame = finalRect;
    } completion:^(BOOL finished) {
        [self.context cancelInteractiveTransition];
    }];
}

@end

第二步：实现interactionControllerForDismissal，返回自定义的可交互动画

#import "AController.h"
#import "BController.h"
#import "PanPresentAnimation.h"
#import "PanDimissAnimation.h"
#import "PanInteractiveTransition.h"

@interface AController ()<UIViewControllerTransitioningDelegate>
@property (nonatomic, strong) PanPresentAnimation *presentAnimation;
@property (nonatomic, strong) PanInteractiveTransition *panInteractiveTransition;
@end

@implementation AController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        _presentAnimation = [PanPresentAnimation new];
        _panInteractiveTransition = [PanInteractiveTransition new];
    }
    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    UIButton *button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(80.0, 210.0, 160.0, 40.0);
    [button setTitle:@"Click me" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}


-(void) buttonClicked:(id)sender {
    BController *mvc =  [[BController alloc] init];
    mvc.transitioningDelegate = self;
    mvc.modalPresentationStyle = UIModalPresentationFullScreen;
    [self.panInteractiveTransition forPresentingViewController:mvc];
    [self presentViewController:mvc animated:YES completion:nil];
}


- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source {
    /// 普通的present转场动画  
    /// 这里个类实现则写了，与present动画方式是一样的，详情请看最后的demo代码
    return self.presentAnimation;
}

-(id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    /// 普通的dimiss转场动画
    return [PanDimissAnimation new];
}

-(id<UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id<UIViewControllerAnimatedTransitioning>)animator {
    /// 这里要判断是否交互触发的dismiss方法，如果不是，则返回nil，表示执行普通dimiss转场动画
    return self.panInteractiveTransition.interacting ? self.panInteractiveTransition : nil;
}
@end

补充：

可交互转场接口UIViewControllerInteractiveTransitioning，系统还提供了”继承于“ UIViewControllerInteractiveTransitioning的接口UIPercentDrivenInteractiveTransition。
UIPercentDrivenInteractiveTransition 做的事跟我们上面自定义的PanInteractiveTransition差不多，主要包括updateInteractiveTransition:、cancelInteractiveTransition、finishInteractiveTransition，有些属性是iOS10之后才引入的，为低版本兼容，就不采用。比如记录是否处于可交互状态wantsInteractiveStart，而是使用自定义的属性。

但是，但是，但是，UIPercentDrivenInteractiveTransition与UIViewControllerInteractiveTransitioning还是很不一样的，官方文档是这样描述的：

备注1：
以animationControllerForDismissedController：方法为例，执行completeTransition:方法时就不能写死YES，需要设置成[transitionContext completeTransition:![transitionContext transitionWasCancelled]];因为交互转场可能取消了，那么就需要返回初始位置

案例：重写上例dismiss可交互返回的动画为例

@interface PanDimissAnimation : NSObject<UIViewControllerAnimatedTransitioning>
@end

@implementation PanDimissAnimation

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {
    return 0.4f;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    NSLog(@"animateTransition: ===== %d",transitionContext.isInteractive);
    /// 原VC
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    /// 跳转VC
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    CGFloat screenW = [UIScreen mainScreen].bounds.size.width;
    /// 获取初始位置
    CGRect initialFrame = [transitionContext initialFrameForViewController:fromVC];
    /// 计算转场最后的位置
    CGRect finalFrame = CGRectOffset(initialFrame, screenW, 0);
    
    /// 都需要将toVC.view添加到视图容器containerView中，不论dismiss动画还是present动画
    /// 将toVC.view 添加到视图容器containerView中
    /// 如果不添加也可以，不过效果不好，在切换的时候，会有一小段是白屏
    /// 推荐添加，并且要置于底部，否则会覆盖在fromVC.view 上面
    [transitionContext.containerView addSubview:toVC.view];
    [transitionContext.containerView sendSubviewToBack:toVC.view];
    
    [UIView animateWithDuration:[self transitionDuration:transitionContext]
                     animations:^{
        /// 设置最后的位置
        fromVC.view.frame = finalFrame;
    } completion:^(BOOL finished) {
        /// 动画完成
        /// （1）completeTransition调用如果返回YES，则会将fromVC.view 从ContainView中移除
        /// 而这里是否完成通过![transitionContext transitionWasCancelled]赋值，
        /// 因为对于可交互动画，是有可能被取消的，那么就需要把fromVC.view复原原来的位置，不能移除
        /// （当可交互动画是继承于UIPercentDrivenInteractiveTransition就会出现这种情况）
        /// （2）如果是没有可交互的动画，那么直接返回YES也是可以，但是推荐使用第一种方式
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}
@end

@interface PanPercentIinteractiveTransition : UIPercentDrivenInteractiveTransition
/// 是否处于交互的状态
@property (nonatomic, assign) BOOL interacting;
/// 用于为B界面添加拖动手势
/// @param viewController BController
- (void)forPresentingViewController:(UIViewController *)viewController;
@end


@interface PanPercentIinteractiveTransition()
@property (nonatomic, strong) UIViewController *presentingViewController;
@end

@implementation PanPercentIinteractiveTransition

/// 用于为B界面添加拖动手势
/// @param viewController BController
- (void)forPresentingViewController:(UIViewController *)viewController {
    self.presentingViewController = viewController;
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc]initWithTarget:self action:@selector(handleGesgture:)];
    [viewController.view addGestureRecognizer: pan];
}

/// 拖动手势响应
- (void)handleGesgture:(UIPanGestureRecognizer *)pan {
    CGPoint translation = [pan translationInView:pan.view.superview];
    CGFloat persent = translation.x / [UIScreen mainScreen].bounds.size.width;
    if (persent < 0) {
        return;
    }
    persent = fabs(persent);
    NSLog(@"========== persent:%f",persent);
    switch (pan.state) {
        /// 手势开始
        case UIGestureRecognizerStateBegan: {
            /// 标记：交互中
            self.interacting = YES;
            /// 执行dismiss方法
            [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
        }
            break;
        /// 拖动中
        case UIGestureRecognizerStateChanged: {
            NSLog(@"update=====");
            /// 更新转场动画进度
            [self updateInteractiveTransition:persent];
        }
            break;
        /// 拖动结束
        case UIGestureRecognizerStateEnded:
        /// 拖动取消、中断
        case UIGestureRecognizerStateCancelled: {
            /// 标记：交互结束
            self.interacting = NO;
            /// 如果滑动查过50%，则返回，否则取消返回原点
            if (persent > 0.5) {
                [self finishInteractiveTransition];
            }else{
                [self cancelInteractiveTransition];
            }
        }
            break;
        default:
            break;
    }
}

@end

DEMO

Present/Dimiss 代码
链接: https://pan.baidu.com/s/1hkR_mhB2AsOq9hu82n-nOQ 密码: 612k

第二节：导航栏转场动画自定义

由第一节已经知道自定义转场动画的流程及设计的类、接口等，其实导航栏转场与模态转场自定义也是一样的基本原理，不同的是变成设置UINavigationController实例的delegate(UINavigationControllerDelegate)，其余的都是一样，这里就不展开细讲🙅‍♂️。

/// 设置转场动画，如果返回nil，则使用系统默认的导航栏转场动画，不论PUSH或POP
/// UINavigationControllerOperation 枚举
/// UINavigationControllerOperationNone, //无
/// UINavigationControllerOperationPush, //push操作
/// UINavigationControllerOperationPop,  //pop操作
- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC  API_AVAILABLE(ios(7.0));

/// 设置可交互动画
- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController API_AVAILABLE(ios(7.0));

第三节：tabBarController切换转场动画自定义

UITabBarController也是自定义转场动画的，套路一样，只是delegate不同(UITabBarControllerDelegate)

/// 普通转场
- (nullable id <UIViewControllerAnimatedTransitioning>)tabBarController:(UITabBarController *)tabBarController
            animationControllerForTransitionFromViewController:(UIViewController *)fromVC
                                              toViewController:(UIViewController *)toVC  API_AVAILABLE(ios(7.0));

/// 可交互转场
- (nullable id <UIViewControllerInteractiveTransitioning>)tabBarController:(UITabBarController *)tabBarController
                      interactionControllerForAnimationController: (id <UIViewControllerAnimatedTransitioning>)animationController API_AVAILABLE(ios(7.0));

解惑：ContainerView

相信你在看文章的时候，一定有个疑惑，到底containerView是什么鬼？是临时的视图容器么？它跟FromVC.view 与 ToVC.view 之间的视图层级关系到底是怎么样？(这很重要，很关键，对于自定义转场动画有很大的帮助)
笔者刚开始的时候也是有很大的疑惑，接下来以 A PUSH B为例，Demo代码下载地
链接: https://pan.baidu.com/s/1Usk2KtjoLu2PenGusVZ3ig 密码: tceb

从上图可以看到containView是一直存在的(UINavigationController、UITabBarController、UIWindow都是带有一个转场视图UITransitionView，用于展示转场动画及控制器视图的)，所以上文自定义转场动画中提到一定要将toVIewController.view 添加到ContainerView中。

参考文章

WWDC 2013 Session笔记 - iOS7中的ViewController切换
iOS自定义转场动画
【实战】快速集成自定义转场动画&手势驱动
iOS 自定义转场动画浅谈
iOS自定义转场动画（push、pop动画）
iOS 两行代码实现自定义转场动画
使用 UIPercentDrivenInteractiveTransition