类似present的push动画

最近项目中有一个视频回放页，一期的时候直接present了一个controller，然后加载播放器进行视频的回放。二期的时候加了新的需求，可以从回放页面继续下一级跳转，但是由于回放页面是present进来的，导致后面的push和present出现诸多问题。所以自己就尝试着，重写NavgationController的转场动画，用push模拟出present的动画效果。

这里用到了UIViewControllerAnimatedTransitioning和UINavigationControllerDelegate两个系统协议，在需要VC切换的时候系统会向实现了UIViewControllerAnimatedTransitioning协议的对象询问是否需要使用自定义的切换效果，重头戏就在这里：

有push就有对应的pop，所以我们首先实现两个PushAnimator。

import UIKit
class PushAnimation: NSObject, UIViewControllerAnimatedTransitioning {
    //设置push动画的周期为0.25s
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.25
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
         //就是push操作后即将显示的controller
        let toController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as! PopController
         //containerView是一个装载view的容器，转场动画中我们所看见的视图，其实都是add在containerView上
        let containerView = transitionContext.containerView
         //toView的最终大小，默认是全屏大小
        let toViewFinalFrame = transitionContext.finalFrame(for: toController)
        //获取toView，同样还可以用UITransitionContextViewKey.from获取fromView
        let toView = transitionContext.view(forKey: UITransitionContextViewKey.to)
         //动画还未开始的时候，让toView在屏幕下方，这样开启动画后，才会有从下往上的一个动画过程
        toView?.frame = CGRect(x: 0, y: UIScreen.main.bounds.height, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
//将toView添加到containerView上
        if toView != nil {
            containerView.addSubview(toView!)
        }
       //开始启动动画
        UIView.animate(withDuration: transitionDuration(using: transitionContext), delay: 0, options: .curveEaseInOut, animations: { 
            toView?.frame = toViewFinalFrame
        }) { _ in
          //动画完成后调用，会从containerView删除fromView  
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
}

接下来就是popAnimator,代码稍稍有差别

import UIKit

import UIKit

class PopAnimation: NSObject, UIViewControllerAnimatedTransitioning {
    
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        return 0.25
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        let toController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as! PushController
        let containerView = transitionContext.containerView
        let toViewFinalFrame = transitionContext.finalFrame(for: toController)
        let toView = transitionContext.view(forKey: UITransitionContextViewKey.to)
        let fromView = transitionContext.view(forKey: UITransitionContextViewKey.from)
        if toView != nil {
            //因为需要fromView从上到下然后消失，最后就显示了toView，所以需要将toView放在containerView的最下面
            containerView.addSubview(toView!)
            containerView.sendSubview(toBack: toView!)
        }
        UIView.animate(withDuration: transitionDuration(using: transitionContext), delay: 0, options: .curveEaseInOut, animations: {
            toView?.frame = toViewFinalFrame
            //fromView从上到下进行一个位移动画，不需要removeFromSuperView
            fromView?.frame = CGRect(x: 0, y: UIScreen.main.bounds.height, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
        }) { _ in
            //执行这句话系统会从containerView上移除fromView
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
        }
    }
}

第二步是实现UINavigationControllerDelegate协议，分别在push和pop的时候选择合适的Animator进行转场

import UIKit

class NavigationAnimationDelegate: NSObject, UINavigationControllerDelegate {

    func navigationController(_ navigationController: UINavigationController, animationControllerFor operation: UINavigationControllerOperation, from fromVC: UIViewController, to toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        if fromVC is PushController && operation == .push  {
            return PushAnimation()
        } else if operation == .pop && fromVC is PopController {
            return PopAnimation()
        } else {
            return nil
        }
    }
}

demo源码