iOS自定义转场动画

在iOS程序里出现得最多的转场动画，就是UINavigationController的Push和Pop了，看多了就觉得有些无聊了，还好苹果提供了自定义转场动画的API，往下看。

首页，要明白既然转场动画是通过导航控制器来完成（UIViewController模态除外），那么就往UINavigationController看，既然是转场，那么在两个控制器切换的中间，就是转场动画发生的地方，一提到“将要出现”，“已经出现”，“将要消失”，“已经消失”，条件反射就想到了UINavigationController的代理方法：

@protocol UINavigationControllerDelegate <NSObject>

@optional

// Called when the navigation controller shows a new top view controller via a push, pop or setting of the view controller stack.
- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated;
- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated;

- (NSUInteger)navigationControllerSupportedInterfaceOrientations:(UINavigationController *)navigationController NS_AVAILABLE_IOS(7_0);
- (UIInterfaceOrientation)navigationControllerPreferredInterfaceOrientationForPresentation:(UINavigationController *)navigationController NS_AVAILABLE_IOS(7_0);

- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController NS_AVAILABLE_IOS(7_0);

- (id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC  NS_AVAILABLE_IOS(7_0);

@end

注意最后两个方法，就是它了，注意可用的iOS版本：NS_AVAILABLE_IOS(7_0)

- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController NS_AVAILABLE_IOS(7_0);

这个方法是讲的手势百分比交互，今天不谈，说最后一个方法，它的返回值是

id <UIViewControllerAnimatedTransitioning>，一个遵循UIViewControllerAnimatedTransitioning的对象，点开它：

@protocol UIViewControllerAnimatedTransitioning <NSObject>

// This is used for percent driven interactive transitions, as well as for container controllers that have companion animations that might need to
// synchronize with the main animation. 
- (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext;
// This method can only  be a nop if the transition is interactive and not a percentDriven interactive transition.
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;


@optional

两个方法，第一个是返回动画持续时间，第二个是动画具体内容。

说了这么多理论，总结一下自定义转场动画大致的设置思路：

1、自定义一个继承自NSObject并且遵从UIViewControllerAnimatedTransitioning协议的类，里面实现协议方法，设置好动画时长和具体内容；

2、在转场动画发生的viewcontroller里，遵从UINavigationControllerDelegate协议，实现协议方法

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC

在该方法里返回自定义的动画类的一个对象即可。

示例：

新建一个有两个viewcontroller的工程：FirstViewController、SecondViewcontroller，将FirstViewcontroller加到一个导航控制器里，它的view上有一个“push”按钮，点它可以将SecondViewController push进来，SecondViewController上有一个“pop”按钮，点它可以pop到FirstViewController，描述得已经很清楚了吧。

创建两个继承自NSObject的类，一个叫PushAnimation，一个叫PopAnimation，它们都遵循UIViewControllerAnimatedTransitioning协议：

@interface PushAnimation : NSObject<UIViewControllerAnimatedTransitioning>

@end

@interface PopAnimation : NSObject<UIViewControllerAnimatedTransitioning>

@end

在PushAnimation.h

//返回动画持续时间
- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext
{
    return 2.0f;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    //获取起点controller
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    
    //获取终点controller
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    //获取转场容器视图
    UIView *containerView = [transitionContext containerView];
    
    //设置终点视图的frame
    CGRect frame = [transitionContext initialFrameForViewController:fromVC];
    CGRect offScreenFrame = frame;
    //先将其设置到屏幕外边，通过动画进入
    offScreenFrame.origin.x = offScreenFrame.size.width;
    toVC.view.frame = offScreenFrame;
    
    //添加视图
    [containerView addSubview:toVC.view];
    
    //执行动画
    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        //设置缩放和透明度
        fromVC.view.transform = CGAffineTransformMakeScale(0.8, 0.8);
        fromVC.view.alpha = 0.5;
        //设置位置
        toVC.view.frame = frame;
    } completion:^(BOOL finished) {
        fromVC.view.transform = CGAffineTransformIdentity;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
        }];
}

在PopAnimation里实现下面方法（push的逆动画，其实可以只创建一个类，通过“顺”or“逆”来判断执行的动画）：

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext
{
    return 2.0f;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
{
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    UIView *containerView = [transitionContext containerView];
    
    toVC.view.transform = CGAffineTransformMakeScale(0.8, 0.8);
    toVC.view.alpha = 0.5;
    CGRect frame = [transitionContext initialFrameForViewController:fromVC];
    CGRect offScreenFrame = frame;
    offScreenFrame.origin.x = offScreenFrame.size.width;
    
    [containerView insertSubview:toVC.view belowSubview:fromVC.view];
    
    
    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        toVC.view.transform = CGAffineTransformIdentity;
        toVC.view.alpha = 1.0f;
        fromVC.view.frame = offScreenFrame;
    } completion:^(BOOL finished) {
        fromVC.view.transform = CGAffineTransformIdentity;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
    }];
}

在FirstViewController.m里添加下面代码：

#import "PushAnimation.h"

@interface FirstViewController ()<UINavigationControllerDelegate>
{
    PushAnimation *_pushAni;
}
@end

- (void)viewDidLoad {
    [super viewDidLoad];
    _pushAni = [PushAnimation new];
}

- (void)viewDidAppear:(BOOL)animated
{
    self.navigationController.delegate = self;
    [super viewDidAppear:animated];
}

- (void)viewDidDisappear:(BOOL)animated
{
    if (self.navigationController.delegate == self) {
        self.navigationController.delegate = nil;
    }
    [super viewDidDisappear:animated];
}

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
    if (operation == UINavigationControllerOperationPush) {
        return _pushAni;
    }
    return nil;
}

同样，在SecondViewController里设置pop的动画代码，即可，更好的方法，可以写一个继承自UINavigationController的子类，统一实现协议方法。