iOS 自定义转场

自定义转场可以分为push/pop、present/dismiss、UITabbarController三种，本文只描述前两种，并提供大体思路。
在视图控制器中自定义push/pop转场：

遵循导航代理：
self.navigationController.delegate = self;
添加代理：
<UINavigationControllerDelegate>
实现代理方法：
// 点击返回按钮，需实现：
- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC 
// 若通过手机屏幕左侧向右滑动实现返回，需实现
- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController

第一个代理方法需要返回一个遵循UIViewControllerAnimatedTransitioning代理的对象：

@protocol UIViewControllerAnimatedTransitioning <NSObject>

- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;

@optional

- (id <UIViewImplicitlyAnimating>) interruptibleAnimatorForTransition:(id <UIViewControllerContextTransitioning>)transitionContext NS_AVAILABLE_IOS(10_0);

- (void)animationEnded:(BOOL) transitionCompleted;

@end

我们只需实现前两个代理方法，
第一个代理方法设置动画时间。
第二个代理方法设置具体实现动画内容。

对于interactionControllerForAnimationController代理方法，需要返回遵循UIViewControllerInteractiveTransitioning代理的对象,
我们可以直接创建遵循UIViewControllerInteractiveTransitioning代理对象实现，
也可以创建继承UIPercentDrivenInteractiveTransition的对象，
UIPercentDrivenInteractiveTransition是苹果对UIViewControllerInteractiveTransitioning代理的封装。
具体代码可以参考下面的Demo。

在视图控制器中自定义present/dismiss转场：

遵循过渡代理：
nextvc.modalPresentationStyle = UIModalPresentationCustom;
nextvc.transitioningDelegate = self;
添加代理：
<UIViewControllerTransitioningDelegate>
实现代理方法：
@protocol UIViewControllerTransitioningDelegate <NSObject>

@optional
// 动画present
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source;

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

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

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

// 自定义弹窗管理
- (nullable UIPresentationController *)presentationControllerForPresentedViewController:(UIViewController *)presented presentingViewController:(nullable UIViewController *)presenting sourceViewController:(UIViewController *)source NS_AVAILABLE_IOS(8_0);

@end

我们可以选择前四个方法中的多个方法进行实现，返回对象类型与自定义push/pop转场一致，所以实现也是一样的。

具体实现动画的代码，可以参考下面的两个Demo中的例子。

参考链接：
自定义present、dismiss 带交互
iOS自定义转场动画-无交互
Demo:
HHTransition
VCTransitionsLibrary