iOS：探究視圖控制器的轉場動畫

一、介紹在iOS開發中，轉場動畫的使用無處不見，不只是我們自己更多的使用UIViewblock動畫實現一個轉場動畫，其實，在我們實現VC控制器跳轉的時候都是轉場動畫的實現，例如標簽欄控制器的切換、模態動畫present和dismiss、導航控制器的push和pop。實現它們的轉場動畫，只需要實現它 ...

一、介紹

在iOS開發中，轉場動畫的使用無處不見，不只是我們自己更多的使用UIViewblock動畫實現一個轉場動畫，其實，在我們實現VC控制器跳轉的時候都是轉場動畫的實現，例如標簽欄控制器的切換、模態動畫present和dismiss、導航控制器的push和pop。實現它們的轉場動畫，只需要實現它們的動畫協議即可，說起來有點太籠統，不如看下麵的圖吧：

二、分析

對於上面的三種類型的控制器，系統都會為它們設置一個代理，通過這個代理方法去監測它們切換VC的過程，這個過程僅僅是出現和消失的過程，至於這個過程是什麼過渡效果，這個代理是不管的。要想這個過程是有動畫的，那麼在這些過程中，也就是代理函數中，需要另外再返回一個實現動畫的對象，這個對象必須遵循實現動畫的協議，在這個協議中開發者可以重寫自定義轉場動畫。下麵會慢慢演示這三種類型控制器的自定義轉場動畫。

重寫不可交互轉場動畫的核心協議內容：

//重寫動畫協議
@protocol UIViewControllerAnimatedTransitioning <NSObject>

//動畫執行時間
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;

//自定義動畫效果
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@end

重寫可交互轉場動畫的核心協議內容：

//重寫動畫協議
@protocol UIViewControllerInteractiveTransitioning <NSObject>

//自定義動畫效果
- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@end

系統提供的一個百分比可交互轉場動畫核心類內容：

//系統提供的百分比動畫類，已經遵循了可交互協議
@interface UIPercentDrivenInteractiveTransition : NSObject <UIViewControllerInteractiveTransitioning>

- (void)pauseInteractiveTransition;
- (void)updateInteractiveTransition:(CGFloat)percentComplete;
- (void)cancelInteractiveTransition;
- (void)finishInteractiveTransition;

@end

三、轉場動畫View之間的切換

四、實現一個自定義的模態動畫

1、概述

正如我們所知，系統為我們提供的模態動畫預設是從底部present出，然後dismiss回到底部。雖然說這個基本能夠滿足使用，但是如果我們還想使用其他形式的模態動畫例如從頂部present出dismiss回到頂部，這個時候就需要對系統預設的轉場動畫進行自定義了。

2、詳解

（1）要自定義模態轉場動畫，首先需要給被模態的控制器設置一個實現了UIViewControllerAnimatedTransitioning協議的代理，這些協議方法可以監測動畫執行的過程，代理和協議如下：

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

//協議
@protocol UIViewControllerTransitioningDelegate <NSObject>
@optional
//present時調用，返回一個實現了不可交互轉場動畫協議的代理
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

//dismiss時調用，返回一個實現了不可交互轉場動畫協議的代理
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed;

//presnt過程中交互時調用，返回一個實現了可交互的轉場動畫協議的代理
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

//dismiss過程中交互時調用，返回一個實現了可交互的轉場動畫協議的代理
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

//返回新的模態彈框控制器（這個是對模態風格進行自定義時調用，後面會說到）
- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(nullable UIViewController *)presenting sourceViewController:(UIViewController *)source API_AVAILABLE(ios(8.0));
@end

（2）然後在上面的協議方法中返回一個實現了UIViewControllerAnimatedTransitioning協議的代理，在這個代理的協議方法中可以真正重寫轉場動畫了，協議如下：

@protocol UIViewControllerAnimatedTransitioning <NSObject>
//動畫執行時間
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
//自定義轉場動畫
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;
@optional

（3）自定義轉場動畫實現如下【註意：Singleton單例類和UIView+Extesion分類需要自己去拷貝引入】

設置UIViewControllerAnimatedTransitioning代理對象TransitionDelegate，監測動畫執行過程，將其設置為單例

#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>

//展示的動畫
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
{
    CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
    animation.presented = YES;
    return animation;
}

//關閉的動畫
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
{
    CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
    animation.presented = NO;
    return animation;
}
@end

設置UIViewControllerAnimatedTransitioning代理對象CustomTransitionAnimationTransition，重寫動畫效果

#import <UIKit/UIKit.h>

@interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
//判斷是present還是dismiss, YES:present  NO:dismisss
@property (assign,nonatomic)BOOL presented;
@end

//設置過渡動畫（modal和dismiss的動畫都需要在這裡處理）
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    // UITransitionContextToViewKey,
    // UITransitionContextFromViewKey.
    
    //出來的動畫
    if (self.presented) {
        
        //獲取並添加轉場視圖
        UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
        [transitionContext.containerView addSubview:toView];
         
        //設置動畫從上往下出來
        toView.y = -toView.height;
        
        [UIView animateWithDuration:duration animations:^{
            
            toView.y = 0;
            
        } completion:^(BOOL finished) {
            
            //移除視圖
            BOOL cancle = [transitionContext transitionWasCancelled];
            if (cancle) {
                [toView removeFromSuperview];
            }
            
            //動畫完成後,視圖上的事件才能處理
            [transitionContext completeTransition:!cancle];
        }];
    }
    //銷毀的動畫
    else
    {
        //獲取轉場視圖
        UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
        
        [UIView animateWithDuration:duration animations:^{
            
            fromView.y = -fromView.height;

        } completion:^(BOOL finished) {
            
            //移除視圖
            BOOL cancle = [transitionContext transitionWasCancelled];
            if (!cancle) {
                [fromView removeFromSuperview];
            }
            
            //動畫完成後,視圖上的事件才能處理
            [transitionContext completeTransition:!cancle];
        }];
    }
}

開始執行，結果如gif圖

//present
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
nav.transitioningDelegate = [TransitionDelegate sharedTransitionDelegate];//自定義轉場動畫
nav.modalPresentationStyle = UIModalPresentationFullScreen;
[self presentViewController:nav animated:YES completion:nil];

（4）我們已經實現了一個簡單的自定義模態不可交互的轉場動畫，其實，在模態控制器的時候，我們還可以自定義可交互的轉場動畫以及設置自定義的模態風格。可交互的轉場動畫一會兒再討論，先來討論一下模態風格，系統在iOS13之前預設都是滿屏模式的UIModalPresentationFullScreen，但是iOS13之後，預設是UIModalPresentationPageSheet。系統提供的模態風格如下：

//模態風格枚舉
typedef NS_ENUM(NSInteger, UIModalPresentationStyle) {
    UIModalPresentationFullScreen = 0,
    UIModalPresentationPageSheet ,
    UIModalPresentationFormSheet ,
    UIModalPresentationCurrentContext ,
    UIModalPresentationCustom , //自定義
    UIModalPresentationOverFullScreen ,
    UIModalPresentationOverCurrentContext ),
    UIModalPresentationPopover ,
    UIModalPresentationBlurOverFullScreen ,
    UIModalPresentationNone,
    UIModalPresentationAutomatic , 
};

（5）從上面的枚舉可以看到，系統是支持我們實現自己的風格的，也就是自定義。在實現自定義之前，一定得知道UIPresentationController這個類，這個是彈出框控制項，模態的控制器都是由它進行管理，主要代碼如下：

//重寫此方法可以在彈框即將顯示時執行所需要的操作
- (void)presentationTransitionWillBegin;

//重寫此方法可以在彈框顯示完畢時執行所需要的操作
- (void)presentationTransitionDidEnd:(BOOL)completed;

//重寫此方法可以在彈框即將消失時執行所需要的操作
- (void)dismissalTransitionWillBegin;

//重寫此方法可以在彈框消失之後執行所需要的操作
- (void)dismissalTransitionDidEnd:(BOOL)completed;

//重寫決定了彈出框的frame
- (CGRect)frameOfPresentedViewInContainerView;

//重寫對containerView進行佈局
- (void)containerViewWillLayoutSubviews;
- (void)containerViewDidLayoutSubviews;

//初始化方法
- (instancetype)initWithPresentedViewController:(UIViewController *)presentedViewController presentingViewController:(UIViewController *)presentingViewController;

（6）額外再提一個知識點，因為一會兒在自定義模態風格時會涉及到。在本文開篇結構圖中介紹了創建的轉場動畫都是在轉場動畫上下文UIViewControllerContextTransitioning協議中完成的，那麼這個轉場動畫的執行是誰管理呢？看結構圖如下，沒錯，是由UIViewControllerTransitionCoordinator這個代理協調器在協調器上下文中完成的，系統給UIViewController提供了一個分類，這個分類持有這個代理協調器，通過這個代理協調器可以拿到執行轉場動畫的方法。最終，我們可以自己添加一些操作與轉場動畫同步執行。

UIViewControllerContextTransitioning協議核心內容

@protocol UIViewControllerTransitionCoordinatorContext <NSObject>
// 執行的屬性
@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 

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

// 參與的視圖
// UITransitionContextToViewKey、UITransitionContextFromViewKey
- (nullable __kindof UIView *)viewForKey:(UITransitionContextViewKey)key API_AVAILABLE(ios(8.0));
@end

UIViewControllerTransitionCoordinator協議核心內容

// 與動畫控制器中的轉場動畫同步，執行其他動畫
- (BOOL)animateAlongsideTransition:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))animation
                        completion:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))completion;
 
// 與動畫控制器中的轉場動畫同步，在指定的視圖內執行動畫
- (BOOL)animateAlongsideTransitionInView:(nullable UIView *)view
                               animation:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))animation
                              completion:(void (^ __nullable)(id <UIViewControllerTransitionCoordinatorContext>context))completion;

UIViewController(UIViewControllerTransitionCoordinator) 分類核心內容

//持有轉場動畫執行協調器
@interface UIViewController(UIViewControllerTransitionCoordinator)
@property(nonatomic, readonly, nullable) id <UIViewControllerTransitionCoordinator> transitionCoordinator;
@end

（7）自定義模態風格實現如下【註意：Singleton單例類和UIView+Extesion分類需要自己去拷貝引入】

設置UIViewControllerAnimatedTransitioning代理對象TransitionDelegate，監測動畫執行過程並返回模態風格，將其設置為單例

#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>
//返回模態風格
-(UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(UIViewController *)presenting sourceViewController:(UIViewController *)source
{
    return [[CustomPresentationController alloc] initWithPresentedViewController:presented presentingViewController:presenting];
}

//展示的動畫
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source
{
    CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
    animation.presented = YES;
    return animation;
}

//關閉的動畫
- (id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed
{
    CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
    animation.presented = NO;
    return animation;
}
@end

設置UIViewControllerAnimatedTransitioning代理對象CustomTransitionAnimationTransition，重寫動畫效果

#import <UIKit/UIKit.h>

@interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
//判斷是present還是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>
//動畫時間
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
{
    return duration;
}

//設置過渡動畫（modal和dismiss的動畫都需要在這裡處理）
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    // UITransitionContextToViewKey,
    // UITransitionContextFromViewKey.    
    
　　 //發現此處並沒有添加toView到containerView中以及從containerView中移除toView，與上面的有區別。
    //我把添加和移除toView的操作放到了下麵的自定義的模態風格類中完成的
    
    //出來的動畫
    if (self.presented) {
         UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    
        //設置動畫從上往下出來
        toView.y = -toView.height;
        
        [UIView animateWithDuration:duration animations:^{
            
            toView.y = 0;
            
        } completion:^(BOOL finished) {
            
            //動畫完成後,視圖上的事件才能處理
            [transitionContext completeTransition:YES];
        }];
    }
    //銷毀的動畫
    else
    {
        [UIView animateWithDuration:duration animations:^{
            
            UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
            
            fromView.y = -fromView.height;
            
        } completion:^(BOOL finished) {
            
            //動畫完成後,視圖上的事件才能處理
            [transitionContext completeTransition:YES];
        }];
    }   
}

設置自定義的模態風格類CustomPresenttationController

#import "CustomPresentationController.h"

@implementation CustomPresentationController

//可以改變被模態的控制器視圖的尺寸
- (CGRect)frameOfPresentedViewInContainerView
{
　　 //CGRectInset: 在containerView的frame基礎上，將width減小100，將height減小200
    //containerView是容納presentedView的一個容器
    return CGRectInset(self.containerView.bounds, 50, 100);
}

//將上面重置的frame完成佈局
- (void)containerViewDidLayoutSubviews {
    self.presentedView.frame = self.frameOfPresentedViewInContainerView;
    [super containerViewDidLayoutSubviews];
}

//過渡即將展示時的處理
//這個過程可以改變視圖屬性、或者添加視圖等
- (void)presentationTransitionWillBegin
{
    self.presentedView.frame = self.containerView.frame;
    [self.containerView addSubview:self.presentedView];
}


//過渡展示完成
//做清理工作
- (void)presentationTransitionDidEnd:(BOOL)completed
{
     if (!completed) {
        [self.presentedView removeFromSuperview];
     }
}

//過渡即將消失時的處理
//這個過程可以改變視圖屬性等
- (void)dismissalTransitionWillBegin
{
    //例如改變透明度，與轉場控制器中的轉場動畫同步執行
    [self.presentingViewController.transitionCoordinator animateAlongsideTransition:^(id<UIViewControllerTransitionCoordinatorContext>  _Nonnull context) {
        
        self.presentedView.alpha = 0.f;
        
    } completion:nil];
}

//過渡消失完成
//做清理工作
- (void)dismissalTransitionDidEnd:(BOOL)completed
{
    if (completed) {
        [self.presentedView removeFromSuperview];
    }
}
@end

開始執行，結果如gif圖

//present
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
nav.transitioningDelegate = [TransitionDelegate sharedTransitionDelegate];//自定義轉場動畫
nav.modalPresentationStyle = UIModalPresentationCustom; //自定義模態風格
[self presentViewController:nav animated:YES completion:nil];

（8）自定義模態轉場動畫和自定義模態風格我們都實現完了，但是上面的動畫過程中都是不可交互的，那麼要想實現可交互的動畫該怎麼做呢？如上面所說的，在dismiss時返回一個實現了UIViewControllerInteractiveTransitioning協議的代理或者直接是原生類UIPercentDrivenInteractiveTransition對象。其中，UIPercentDrivenInteractiveTransition是系統封裝好了百分比驅動，用起來很簡單，那麼真正的實現原理還是我們去實現一下。下麵咱們來實現導航模式的交互效果，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 {
    
     //這裡還是採用自定義的轉場動畫方式進行present，使其present時從屏幕右側滑入
     CustomAnimationTransition *animation = [[CustomAnimationTransition alloc]init];
     animation.presented = YES;
     return animation;
}

//dismiss,必須重寫
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    //這裡採用自定義的轉場動畫覆蓋系統的dismiss效果，在dismiss時，由於自定義了交互動畫，所以系統自己的dismiss動畫不會執行
    CustomAnimationTransition *animation = [[CustomAnimationTransition alloc] init];
    animation.presented = NO;
    return animation;
}

//將要dismiss時的交互行為，必須重寫
- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator {
    
    CustomInteractiveTransition *animation = [[CustomInteractiveTransition alloc] init];
    return animation;
}

@end

CustomAnimationTransition

#import <UIKit/UIKit.h>

@interface CustomAnimationTransition : NSObject<UIViewControllerAnimatedTransitioning>
//判斷是present還是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>
//動畫時間
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
{
    return duration;
}

//設置過渡動畫（modal和dismiss的動畫都需要在這裡處理）
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    // UITransitionContextToViewKey,
    // UITransitionContextFromViewKey.
    
    //出來的動畫
    if (self.presented) {
        
        //獲取並添加轉場視圖
        UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
        [transitionContext.containerView addSubview:toView];
         
        //設置動畫從右往左出來
        toView.x = toView.width;

        [UIView animateWithDuration:duration animations:^{

            toView.x = 0;

        } completion:^(BOOL finished) {
            
            //移除視圖
            BOOL cancle = [transitionContext transitionWasCancelled];
            if (cancle) {
                [toView removeFromSuperview];
            }
            
            //動畫完成後,視圖上的事件才能處理
            [transitionContext completeTransition:!cancle];
        }];
    }
    //銷毀的動畫
    else
    {
        //不做處理，而是交給自定義的交互動畫去完成
    }
}
@end

CustomInteractiveTransition

#import <UIKit/UIKit.h>
#import "Singleton.h"

@interface CustomInteractiveTransition : NSObject<UIViewControllerInteractiveTransitioning>
SingletonH(CustomInteractiveTransition); //採用單例的方式主要是為了保存交互上下文

//動畫進度更新
-(void)updateAnimationProgress:(CGFloat)progress;

//動畫完成
-(void)finish;

//動畫取消
-(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

//開始交互時調用
- (void)startInteractiveTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    
    //保存上下文
    self.context = transitionContext;
    
    //更改視圖層級
    UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
    UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
    [transitionContext.containerView insertSubview:toView belowSubview:fromView];
}


//動畫進度更新
-(void)updateAnimationProgress:(CGFloat)progress {
    
    UIView *fromView = [self.context viewForKey:UITransitionContextFromViewKey];
    fromView.x = self.context.containerView.width * progress;
    
}

//動畫完成
-(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];
    }];
}

//動畫取消
-(void)cancel {
    
    UIView *fromView = [self.context viewForKey:UITransitionContextFromViewKey]; 
    [UIView animateWithDuration:0.2 animations:^{

        fromView.x = 0;
        
    } completion:^(BOOL finished) {
       [fromView removeFromSuperView]; 
       [self.context cancelInteractiveTransition];
    }];
}
@end

在被模態的控制器添加拖拽手勢

#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 < 0) {
        return;
    }
    //拖拽的距離進度比
    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

開始執行，結果如gif圖

UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:[[SecondViewController alloc] init]];
nav.transitioningDelegate = [TransitioningDelegate sharedTransitioningDelegate];//自定義可交互轉場動畫
nav.modalPresentationStyle = UIModalPresentationFullScreen; //系統模態風格
[self presentViewController:nav animated:YES completion:nil];

五、實現一個自定義的導航動畫

1、重寫導航控制器的協議，返回自定義的導航轉場動畫，動畫實現的方式和modal思想一致，重寫的核心協議如下：

//重寫導航控制器協議
@protocol UINavigationControllerDelegate <NSObject>
@optional
................

//返回一個實現了自定義交互動畫的對象
- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController;


//返回一個實現了普通動畫的對象
- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC;
@end

2、現在就來自定義一個導航轉場動畫，步驟如下：

創建一個CustomNavigationTransition類，實現導航控制器的協議

#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

//返回一個實現了普通動畫的對象
- (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

自定義一個CustomNavigationAnimation類，實現動畫協議，重寫動畫效果

#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@inte