iOS(视图控制器转场)

转场需要提供转场代理，不使用默认的代理则需要自己实现代理方式，有UINavigationController、UITabBarController、UIViewController三种代理，实现以下三种协议
<UINavigationControllerDelegate> 　　　　//push和pop切换
<UITabBarControllerDelegate> 　　　　　　//tab切换
<UIViewControllerTransitioningDelegate> 　//UICollectionViewController 与 UINavigationController 结合的转场方式

转场触发时，需要UIKit 将要求转场代理将提供转场动画的核心构件:动画控制器和交互控制器


动画控制器(Animation Controller)：

　最重要的部分，负责添加视图以及执行动画;遵守<UIViewControllerAnimatedTransitioning>协议；由我们实现。

　　

　交互控制器

　通过交互手段，通常是手势来驱动动画控制器实现的动画，使得用户能够控制整个过程；遵守<UIViewControllerInteractiveTransitioning>协议；系统已经打包好现成的类供我们使用

   转场环境(Transition Context):

提供转场中需要的数据；遵守<UIViewControllerContextTransitioning>协议；由 UIKit 在转场开始前生成并提供给我们提交的动画控制 器和交互控制器使用。

　　

转场协调器(Transition Coordinator)：

可在转场动画发生的同时并行执行其他的动画，其作用与其说协调不如说辅助，主要在 Modal 转场和交互转场取消时使用，其他时候很少用到；遵守<UIViewControllerTransitionCoordinator>协议；由 UIKit 在转场时生成，UIViewController 在 iOS 7 中新增了方法transitionCoordinator()返回一个遵守该协议的对象，且该方法只在该控制器处于转场过程中才返回一个此类对象，不参与转场时返回 nil

动画控制器协议实现:
　

//返回动画时间

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext {

return self.duration;

}

//执行动画

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

//返回容器视图,转场发生的地方

//获取参与转场的视图控制器，有 UITransitionContextFromViewControllerKey 和 UITransitionContextToViewControllerKey 两个 Key。

//通过viewForKey:获取的视图是viewControllerForKey:返回的控制器的根视图，或者 nil。viewForKey:方法返回 nil 只有一种情况： UIModalPresentationCustom 模式下的 Modal 转场 ，通过此方法获取 presentingView 时得到的将是 nil，在后面的 Modal 转场里会详细解释。

UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];

UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

UIView *toView = toVC.view;

UIView *fromView = fromVC.view;

[self animateTransition:transitionContext fromVC:fromVC toVC:toVC fromView:fromView toView:toView];

}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext fromVC:(UIViewController *)fromVC toVC:(UIViewController *)toVC fromView:(UIView *)fromView toView:(UIView *)toView {

// Add the toView to the container

UIView* containerView = [transitionContext containerView];

[containerView addSubview:toView];

[containerView sendSubviewToBack:toView];

CGSize size = toView.frame.size;

NSMutableArray *snapshots = [NSMutableArray new];

CGFloat xFactor = 10.0f;

CGFloat yFactor = xFactor * size.height / size.width;

// snapshot the from view, this makes subsequent snaphots more performant

UIView *fromViewSnapshot = [fromView snapshotViewAfterScreenUpdates:NO];

// create a snapshot for each of the exploding pieces

for (CGFloat x=0; x < size.width; x+= size.width / xFactor) {

for (CGFloat y=0; y < size.height; y+= size.height / yFactor) {

CGRect snapshotRegion = CGRectMake(x, y, size.width / xFactor, size.height / yFactor);

UIView *snapshot = [fromViewSnapshot resizableSnapshotViewFromRect:snapshotRegion  afterScreenUpdates:NO withCapInsets:UIEdgeInsetsZero];

snapshot.frame = snapshotRegion;

[containerView addSubview:snapshot];

[snapshots addObject:snapshot];

}

}

[containerView sendSubviewToBack:fromView];

// animate

NSTimeInterval duration = [self transitionDuration:transitionContext];

[UIView animateWithDuration:duration animations:^{

for (UIView *view in snapshots) {

CGFloat xOffset = [self randomFloatBetween:-100.0 and:100.0];

CGFloat yOffset = [self randomFloatBetween:-100.0 and:100.0];

view.frame = CGRectOffset(view.frame, xOffset, yOffset);

view.alpha = 0.0;

view.transform = CGAffineTransformScale(CGAffineTransformMakeRotation([self randomFloatBetween:-10.0 and:10.0]), 0.01, 0.01);

}

} completion:^(BOOL finished) {

for (UIView *view in snapshots) {

[view removeFromSuperview];

}

[transitionContext completeTransition:![transitionContext transitionWasCancelled]];

}];

}

- (float)randomFloatBetween:(float)smallNumber and:(float)bigNumber {

float diff = bigNumber - smallNumber;

return (((float) (arc4random() % ((unsigned)RAND_MAX + 1)) / RAND_MAX) * diff) + smallNumber;

}

参考链接:http://blog.devtang.com/2016/03/13/iOS-transition-guide/