酷炫的转场动画难的是想象，不是实现。
UIViewControllerTransitioning.h里面包含了所有你想要的
其中 ** UIViewControllerContextTransitioning ** 协议是转场动画上下文，看其属性就能看到，它提供了大多部分转场相关的细节内容
你可以拿到容器视图 ：** containerView() -> UIView? **
还可以拿到动画的主要两个页面：** viewForKey(key: String) -> UIView? **
// viewForKey: may return nil which would indicate that the animator should not
// manipulate the associated view controller's view.
@available(iOS 8.0, *)
public func viewForKey(key: String) -> UIView?
key:UITransitionContextFromViewKey 或者 UITransitionContextToViewKey
在 Modal 转场里要注意，从上面可以知道，Custom 模式下，fromView 并不受 containerView 管理，这时通过viewForKey:方法来获取 fromView 得到的是 nil.但是你可以用下面的方法来搞
获取视图 ** public func viewControllerForKey(key: String) -> UIViewController? **
key:UITransitionContextToViewControllerKey, and UITransitionContextFromViewControllerKey. 再通过.view 来拿到对应的 to/from View
好了 还有常用切很重要的 ** public func completeTransition(didComplete: Bool)
**
动画执行后 必须写上这句话。 还有一个 ** transitionWasCancelled() -> Bool **
下面这些看注释就清楚了，跟交互相关的，在实现交互的时候也就这几个函数。下面细讲
public func isInteractive() -> Bool // This indicates whether the transition is currently interactive.//是否是与用户交互控制的动画
// It only makes sense to call these from an interaction controller that
// conforms to the UIViewControllerInteractiveTransitioning protocol and was
// vended to the system by a container view controller's delegate or, in the case
// of a present or dismiss, the transitioningDelegate.
public func updateInteractiveTransition(percentComplete: CGFloat)
public func finishInteractiveTransition()
public func cancelInteractiveTransition()
实现一个简单的转场动画
1.实现对应的控制器代理方法，简单告诉他返回你已经实现了转场动画协议的类对象，或者实现了交互协议的类对象就好了。 注意如果当前不是交互控制转场的，在转场协议里面要返回nil。
push,pop转场 navi-UINavigationControllerDelegate
@available(iOS 7.0, *)
optional public func navigationController(navigationController: UINavigationController, interactionControllerForAnimationController animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning?
@available(iOS 7.0, *)
optional public func navigationController(navigationController: UINavigationController, animationControllerForOperation operation: UINavigationControllerOperation, fromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning?
selelcted-UITabBarControllerDelegate
@available(iOS 7.0, *)
optional public func tabBarController(tabBarController: UITabBarController, interactionControllerForAnimationController animationController: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning?
@available(iOS 7.0, *)
optional public func tabBarController(tabBarController: UITabBarController, animationControllerForTransitionFromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning?
present,dismiss - transitioningDelegate
@available(iOS 2.0, *)
optional public func animationControllerForPresentedController(presented: UIViewController, presentingController presenting: UIViewController, sourceController source: UIViewController) -> UIViewControllerAnimatedTransitioning?
@available(iOS 2.0, *)
optional public func animationControllerForDismissedController(dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning?
optional public func interactionControllerForPresentation(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning?
optional public func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning?
@available(iOS 8.0, *)
optional public func presentationControllerForPresentedViewController(presented: UIViewController, presentingViewController presenting: UIViewController, sourceViewController source: UIViewController) -> UIPresentationController?
含有interactionControllerForAnimationController是交互协议，animationControllerForDismissedController是告诉代理，转场的时候要返回我自己的转场动画控制器。比如这里我返回了一个已经实现UIViewControllerAnimatedTransitioning的动画控制器
extension PushOneVC:UINavigationControllerDelegate {
func navigationController(navigationController: UINavigationController, animationControllerForOperation operation: UINavigationControllerOperation, fromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
if operation == .Pop && fromVC == self {
return nil
}
let type:CircleTransitionType = operation == .Push ? CircleTransitionType.NavTransitionPush :CircleTransitionType.NavTransitionPop
return CirclePushAnimationController(type: type)
}
2.实现转场动画协议里面的两个方法
class CirclePushAnimationController: NSObject,UIViewControllerAnimatedTransitioning {
//告诉他动画的时常
func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
return 0.5
}
//这个是最主要的，告诉他执行什么动画
func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
...
1.拿到容器视图containerView，fromVC,toVC
2.将要执行动画的视图 toView 加到containerView中，其中fromView 系统已经自动加入.
** 注意，如果当前是present切style是Custom,那么在dismiss的时候就不要加toView了，你可以这样简单理解，一般在转场结束completeTransition后，会自动将fromView从容器中移除。但是Custom类型的时候却没有移除，你可以明显的看到。因此在dismiss的时候，之前的fromView 也就变成了toView。**
3.书写酷炫的动画代码，一般使用UIView 的类方法 animaitonWithDur....，如果对toView/fromView的layer做动画就用CABaseAnimation去做。
4.在completion回调或者animationdidStop中记得写上 completeTransition（ture）很重要
}
}
3.实现手势交互
在每一个需要交互控制转场动画的根图层上加一个pan手势，根据手势的状态或者拖动比例以及系统提供的updateInteractiveTransition(0.7)等方法来控制转场进度。
注意一点要在对应的交互代理方法interactionControllerForPresentation中判断当前是不是正在进行手势交互，如果是的话才返回对应的交互控制器，如果不是的话就返回nil
系统提供了一个手势交互控制器，UIPercentDrivenInteractiveTransition。当然你也可以继承他，写一个自己的手势交互控制器。记得一点，每一个需要交互控制转场动画的视图都需要一个自己的交互手势。如fromVC 和 toVC都应该有一个自己的交互手势。这也不难理解。
下面是手势交互控制转场进度的代码
switch gesture.state {
case .Began :
interation = true
self.startTransition()
case .Changed :
updateInteractiveTransition(percent)
case .Ended :
completionSpeed = 0.99
interation = false
if percent > 0.7 {
finishInteractiveTransition()
}else {
cancelInteractiveTransition()
}
case .Cancelled :
interation = false
completionSpeed = 0.99
cancelInteractiveTransition()
default :
break
}
}
func startTransition() {
switch type {
case .Presente, .Push :
if let closure = config {
closure()//执行nav.pushViewController()或者self.presentViewController
}
case .Pop:
vc?.navigationController?.popViewControllerAnimated(true)
case .Dismiss:
vc?.dismissViewControllerAnimated(true, completion: nil)
}
}
最后说一下，你可以通过使用截图snapshotViewAfterScreenUpdates：NO(YES代表立即刷新视图然后截图),对截图和toView进行动画操作，来做一些cell的转场动画。 你也可以通过layer.mask属性做最上面gif图的转场效果，对这个属性有疑问的，可以百度搜alpha通道，会帮助理解。
Demo下载地址
转场详解
另一篇参考博客