iOS7之转场动画

iOS7添加了转场动画，让我们更加方便的切换控制器。

iOS7 SDK支持两种自定义过渡：自定义视图控制器过渡和交互式视图控制器过渡。

怎么来区分自定义视图控制器过渡和交互式试图控制器过渡呢？

当过渡是时间的函数式，它通常是一个自定义视图控制器过渡，如果他是一个手势识别器或者其他类似事件的函数，它通常是一个交互式视图控制器过渡。

举个例子：
UINavigationController过渡使我们最常见的自定义视图控制器过渡。UIPageViewController过渡不是随着时间进行，它需要跟随我们的手指滑动，所以它是一种交互式视图控制器过渡。

0.自定义视图控制器过渡

0.使用Storyboard来实现自定义视图控制器过渡

我们可以使用连线（segue）的方式，来实现自定义视图控制器过渡，segue有好几种类型，
选择某个segue，我们可以看到下图：

segue1

我们选择自定义这种方式可以看到：

segue2

我们可以指定segue Class 它是一个UIStoryboardSegue子类，我们可以创建一个UIStoryboardSegue子类IYMCustomSegue，填写在这里。

在UIStoryboardSegue里有个perform方法，我们在IYMCustomSegue重写一下：

- (void) perfrom{
//这里实现动画
...
}

下面实现一个自定义push动画：

- (void) perform
{
    UIViewController *sourceViewController =              self.sourceViewController;
    UIViewController *desinationViewController =      self.destinationViewController;

    CGRect sourceRect = sourceViewController.view.frame;
    CGRect desinationViewFromRect =     CGRectMake(sourceRect.origin.x + sourceRect.size.width, sourceRect.origin.y, sourceRect.size.width, sourceRect.size.height);
     desinationViewController.view.frame = desinationViewFromRect;
     desinationViewController.view.alpha = 0;
     [sourceViewController.view.superview addSubview:desinationViewController.view];

     [UIView animateWithDuration:0.3 animations:^{
         sourceViewController.view.alpha = 0.5;
         desinationViewController.view.alpha = 1;
         desinationViewController.view.frame = sourceRect;
     }completion:^(BOOL finished) {
         sourceViewController.view.alpha = 1;
         [desinationViewController.view removeFromSuperview];

         [sourceViewController.navigationController  pushViewController:desinationViewController animated:NO];
    }];
}

1.代码方式实现

自定义试图控制器过渡是由两个协议实现的，即UIViewControllerTransitioningDelegate 和 UIViewControllerAnimatedTransitioning。

我们从A控制器到B控制器，通常有两种方式：一种是presentViewController方式，另一种是pushViewController。

0.使用presentViewController方式:从A控制器present到B控制器

设置B控制器的transitionDelegate为A控制器
在A控制器中实现UIViewControllerTransitioningDelegate协议
实现UIViewControllerAnimatedTransitioning

实现UIViewControllerTransitioningDelegate中的方法：

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

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

这两个方法返回的是一个实现了UIViewControllerAnimatedTransitioning协议的类实例。通过方法名字我们就可以看到它们适用于presentViewController方式。如果自定义过渡效果只有一个视图控制器使用，视图控制器本身就可以实现UIViewControllerAnimatedTransitioning协议，否则，就需要一个单独的继承自NSObject一个单独的类来实现UIViewControllerAnimatedTransitioning协议。

这里我们就实现一个B视图控制器过渡动画，就直接在A控制器中实现UIViewControllerAnimatedTransitioning。

实现UIViewControllerTransitioningDelegate中的方法：

// 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{
    //返回动画时间
    return 1.0f;
}

// This method can only  be a nop if the transition is interactive and not a percentDriven interactive transition.
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
    //动画代码在这里写
    ...

    [transitionContext completeTransition:YES];//必须实现这个方法
}

``- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext```中的transitionContext，我们可以获得：

源控制器即来自哪个视图控制器：

UIViewController *src = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

目标控制器，这里是B控制器:

UIViewController *dest = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

容器视图：

UIView *containerView = [transitionContext containerView];

1.使用pushViewController方式:从A控制器push到B控制器

因为是从A控制器push到B控制器，我们不需要实现UIViewControllerTransitioningDelegate中的方法，我们需要：

0.在A控制器设置UINavigationDelegate 为 self
1.实现UINavigationDelegate
2.实现UIViewControllerAnimatedTransitioning协议

实现UINavigationDelegate中的方法：

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

返回的是一个实现了UIViewControllerAnimatedTransitioning协议的类实例。这个和presentViewController方式一样。

1.交互式视图控制器过渡

要实现一个交互式视图控制器过渡，除了要是上面的动画外，还要告诉交互控制器动画完成了多少，我们只要知道完成了多少百分比，告诉系统，系统就直接给咱们处理了。

通过计算手势/动作事件或其他驱动过渡的事件，可以得出百分比。例如通过UIScreenEdgePanGestureRecognizer边缘返回手势，我们可以通过平移量来查看返回完成了多少。

还是要分成两种，一种是presentViewController方式，另一种是pushViewController。

0.使用presentViewController方式

除了上面presentViewController方式实现的协议方法外，我们还需要实现UIViewControllerTransitioningDelegate中的另外两个方法：

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

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

交互控制器实现了UIViewControllerInteractiveTransitioning协议。交互式过渡的交互控制器都必须是UIPercentDrivenInteractiveTransition实例或者UIPercentDrivenInteractiveTransition子类实例。

UIPercentDrivenInteractiveTransition中以下方法可以完成交互过渡：

- (void)updateInteractiveTransition:(CGFloat)percentComplete;//完成了多少，percentComplete是百分比
- (void)cancelInteractiveTransition;//取消
- (void)finishInteractiveTransition;//完成

例如我们给B控制器（A控制器 present to B控制器），B控制器通过缩放到达A控制器，我们给B控制器视图添加了一个缩放手势UIPinchGestureRecognizer。

上面的UIViewControllerTransitioningDelegate我们返回一个 [[UIPercentDrivenInteractiveTransition alloc] init]实例percentDrivenInteractiveTransition。

- (void) pinchGestureAction:(UIPinchGestureRecognizer*) gestureRecognizer {
    CGFloat scale = gestureRecognizer.scale;
    if(gestureRecognizer.state == UIGestureRecognizerStateBegan) {
         self.percentDrivenInteractiveTransition =[[UIPercentDrivenInteractiveTransition alloc] init];
         self.startScale = scale;
         [self.controller dismissViewControllerAnimated:YES completion:nil];
     }
    if(gestureRecognizer.state == UIGestureRecognizerStateChanged) {
          CGFloat completePercent = 1.0 - (scale/self.startScale);
          [self updateInteractiveTransition:completePercent];//完成了多少百分比
    }
    if(gestureRecognizer.state == UIGestureRecognizerStateEnded) {
        if(gestureRecognizer.velocity >= 0){
            [self cancelInteractiveTransition];//取消
         }else{
             [self finishInteractiveTransition];//完成
         }

         self.percentDrivenInteractiveTransition = nil;
    }

     if(gestureRecognizer.state == UIGestureRecognizerStateCancelled) {
        [self cancelInteractiveTransition];//取消
        self.percentDrivenInteractiveTransition = nil;
    }
}

1.使用pushViewController方式

和present方式不同的一点是，我们使用UINavigationDelegate中的：

- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController

来代替：

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

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

其他的都一样。

2.实现一个完整的例子

单击图片展示大图，返回慢慢缩放到小图，效果如下:

效果

将用到：
0.UINavigationDelegate
1.返回手势
2.交互式过渡效果

0.新建两个控制器

首页：IYMFirstViewController
喵星人：IYMSecondViewController

1.使用Storyboard创建两个视图

Storyboard

0.设置UINavigationDelegate

IYMFirstViewController.m IYMSecondViewController.m分别重写以下方法：

- (void)viewDidAppear:(BOOL)animated {
     [super viewDidAppear:animated];

    // Set outself as the navigation controller's delegate so we're asked for a transitioning object
    self.navigationController.delegate = self;
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    // Stop being the navigation controller's delegate
    if (self.navigationController.delegate == self) {
        self.navigationController.delegate = nil;
    }
}

1.实现UINavigationDelegate

IYMFirstViewController.m中：

- (id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
animationControllerForOperation:(UINavigationControllerOperation)operation
fromViewController:(UIViewController *)fromVC
toViewController:(UIViewController *)toVC{
    if (fromVC == self && [toVC isKindOfClass:[IYMSecondViewController class]]) {
        return self;
    }else {
        return nil;
    }
}

IYMSecondViewController.m

- (id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController{
    return _percentDrivenInteractiveTransition;
}

- (id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
animationControllerForOperation:(UINavigationControllerOperation)operation
fromViewController:(UIViewController *)fromVC
toViewController:(UIViewController *)toVC{
    if (fromVC == self && [toVC isKindOfClass:[IYMFirstViewController class]]) {
        return self;
    }else {
        return nil;
    }
}

其中_percentDrivenInteractiveTransition是一个UIPercentDrivenInteractiveTransition实例，在边缘手势中实例化。

2.实现UIViewControllerAnimatedTransitioning

IYMFirstViewController.m

- (NSTimeInterval) transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext
{
    return 0.3f;//动画时间
}

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{
    IYMFirstViewController *fromViewContrroller = (IYMFirstViewController *)[transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    IYMSecondViewController *toViewController = (IYMSecondViewController *)[transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIView *containerView = [transitionContext containerView];

    UIView *snapshotView = [fromViewContrroller.bottomImageView snapshotViewAfterScreenUpdates:NO];//截图
    CGRect snapshotViewFromRect = [containerView convertRect:fromViewContrroller.bottomImageView.frame fromView:fromViewContrroller.view];//获取在ContainerView中的frame
    snapshotView.frame = snapshotViewFromRect; 
    toViewController.view.frame = [transitionContext finalFrameForViewController:toViewController];
    toViewController.view.alpha = 0;
    [containerView addSubview:toViewController.view];
    [containerView addSubview:snapshotView];
    fromViewContrroller.bottomImageView.hidden = YES;
    toViewController.topImageView.hidden = YES;

    CGRect snapshotViewToRect = [containerView convertRect:toViewController.topImageView.frame fromView:toViewController.view];
    [UIView animateWithDuration:0.3 animations:^{
        toViewController.view.alpha = 1;
        snapshotView.frame = snapshotViewToRect;
    } completion:^(BOOL finished) {
        if (finished) {
            [snapshotView removeFromSuperview];
            fromViewContrroller.bottomImageView.hidden = NO;
            toViewController.topImageView.hidden = NO;

            [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
        }
    }];
}