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】
#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
#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 = 0; } 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]; }]; } }
//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 = 0, 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】
#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
#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.
//返现此处并没有添加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 = 0; } 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]; }]; } }
#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, 50, 100); } //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 = 0.f; } completion:nil]; } //过渡消失完成 //做清理工作 - (void)dismissalTransitionDidEnd:(BOOL)completed { if (completed) { [self.presentedView removeFromSuperview]; } } @end
//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：
#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
#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 = 0; } 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:!canc
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