簡(jiǎn)介

上一篇文章蝴蜓，我們討論了UIPresentationController鞭缭，實(shí)現(xiàn)了初步的過場(chǎng)動(dòng)畫自定義受神，也就是背景逐漸顯示抛猖，逐漸影藏。還有就是點(diǎn)擊蒙板退出鼻听，內(nèi)容高度自定義（不是全屏）财著。不過用下來還有以下幾個(gè)問題：
（1）加載是，從下到上的彈出很快就結(jié)束了撑碴，而背景蒙板的逐漸顯示時(shí)間較長(zhǎng)撑教。這是因?yàn)閺南碌缴系膹棾鰟?dòng)畫還是系統(tǒng)默認(rèn)的行為，時(shí)間較短醉拓，大約0.3秒左右伟姐。而蒙板的逐漸顯示是自定義的動(dòng)畫行為，我設(shè)置了較長(zhǎng)時(shí)間（3秒）亿卤，想看清楚一點(diǎn)愤兵。
（2）退出時(shí)，更加明顯排吴，從上到下的退出很快秆乳，而背景蒙板的逐漸隱藏幾乎看不到。隨著系統(tǒng)默認(rèn)動(dòng)畫較快地退出，containerView都被系統(tǒng)收回了屹堰，其子視圖的動(dòng)畫當(dāng)然消失了肛冶。

實(shí)現(xiàn)自定義動(dòng)畫

• 現(xiàn)在不想要系統(tǒng)的從下到上的動(dòng)畫，而是實(shí)現(xiàn)從右到左的動(dòng)畫扯键。

• 統(tǒng)一時(shí)間長(zhǎng)度淑趾，讓視圖的進(jìn)場(chǎng)動(dòng)畫和背景蒙板顯示動(dòng)畫同步。

統(tǒng)一參數(shù)

（1） 動(dòng)畫結(jié)束后忧陪，最終vc的frame需要確定扣泊，這個(gè)當(dāng)做參數(shù)放入公共的代理對(duì)象中（就是那個(gè)default單例）

（2）動(dòng)畫的時(shí)長(zhǎng)，幾個(gè)相關(guān)的對(duì)象都要用統(tǒng)一的參數(shù)嘶摊，這個(gè)也放在代理對(duì)象中

class TempTransitionDelegate: NSObject {
    /// 默認(rèn)單例
    public static let `default`: TempTransitionDelegate = {
        LogUtil.doPrint("TempTransitionDelegate `default` 實(shí)例被創(chuàng)建")
        return TempTransitionDelegate()
    }()
    
    /// 設(shè)置彈窗視圖的高度
    public var sheetHeight: CGFloat = 500
    let phoneWidth = UIScreen.main.bounds.width
    let phoneHeight = UIScreen.main.bounds.height
    var contentFrame: CGRect {
        CGRect(origin: CGPoint(x: 0, y: (phoneHeight - sheetHeight)), size: CGSize(width: phoneWidth, height: sheetHeight))
    }
    
    /// 設(shè)置動(dòng)畫時(shí)間（秒）
    public var animateDuration: TimeInterval = 3
}

自定義動(dòng)畫

• 自定義對(duì)話延蟹，需要一個(gè)實(shí)現(xiàn)了UIViewControllerAnimatedTransitioning的對(duì)象

@MainActor public protocol UIViewControllerAnimatedTransitioning : NSObjectProtocol {

    // 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.
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval

    // This method can only be a no-op if the transition is interactive and not a percentDriven interactive transition.
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning)

• 這兩個(gè)函數(shù)都涉及到一個(gè)參數(shù)UIViewControllerContextTransitioning，這是動(dòng)畫過程中叶堆，系統(tǒng)給的一些有用信息

@MainActor public protocol UIViewControllerContextTransitioning : NSObjectProtocol {
    // The view in which the animated transition should take place.
    @available(iOS 2.0, *)
    var containerView: UIView { get }

    // This must be called whenever a transition completes (or is cancelled.)
    // Typically this is called by the object conforming to the
    // UIViewControllerAnimatedTransitioning protocol that was vended by the transitioning
    // delegate.  For purely interactive transitions it should be called by the
    // interaction controller. This method effectively updates internal view
    // controller state at the end of the transition.
    func completeTransition(_ didComplete: Bool)
}

    // Currently only two keys are defined by the
    // system - UITransitionContextToViewControllerKey, and
    // UITransitionContextFromViewControllerKey. 
    // Animators should not directly manipulate a view controller's views and should
    // use viewForKey: to get views instead.
    @available(iOS 2.0, *)
    func viewController(forKey key: UITransitionContextViewControllerKey) -> UIViewController?

containerView可以和UIPresentationController中的一樣理解阱飘，簡(jiǎn)單講就是一個(gè)全屏的容器。
completeTransition在動(dòng)畫結(jié)束的時(shí)候調(diào)用一下虱颗，告訴系統(tǒng)過場(chǎng)動(dòng)畫結(jié)束了沥匈。
viewController比較特殊，通過from和to兩個(gè)key忘渔，得到不同的VC高帖。進(jìn)場(chǎng)時(shí)，我們顯然是需要toVC畦粮；而消失時(shí)散址，我們是需要fromVC。（多么腦殘的人才能想出這種API宣赔？）

• 所以预麸，除了frame和動(dòng)畫時(shí)長(zhǎng)，我們還需要一個(gè)參數(shù)isPresent來區(qū)分是載入還是退出儒将。這兩者的動(dòng)畫方向是不一樣的吏祸。

• 考慮了以上因素后，代碼大致如下：

class TempAnimate: NSObject {
    /// 載入還是退出的標(biāo)志
    public var isPresent = true
    
    /// 視圖最終的frame
    public var frame: CGRect = UIScreen.main.bounds
    
    /// 動(dòng)畫時(shí)長(zhǎng)
    public var duration: TimeInterval = 0.3
}

extension TempAnimate: UIViewControllerAnimatedTransitioning {
    func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
        duration
    }
    
    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
        /// 獲取源視圖控制器和目標(biāo)視圖控制器的視圖
        let fromVC = transitionContext.viewController(forKey: .from)!
        let toVC = transitionContext.viewController(forKey: .to)!
  
        /// 獲取容器視圖钩蚊，即動(dòng)畫發(fā)生的視圖
        let containerView = transitionContext.containerView
        
        if isPresent {
            /// 進(jìn)場(chǎng)動(dòng)畫從右向左進(jìn)入屏幕贡翘，取toVC
            containerView.addSubview(toVC.view)
            toVC.view.frame = frame.offsetBy(dx: UIScreen.main.bounds.width, dy: 0)
            UIView.animate(withDuration: transitionDuration(using: transitionContext)) {
                toVC.view.frame = self.frame
            } completion: { _ in
                transitionContext.completeTransition(true)
            }
        } else {
            /// 退出動(dòng)畫從右向左離開屏幕，取fromVC
            containerView.addSubview(fromVC.view)
            fromVC.view.frame = frame
            UIView.animate(withDuration: transitionDuration(using: transitionContext)) {
                fromVC.view.frame = self.frame.offsetBy(dx: -UIScreen.main.bounds.width, dy: 0)
            } completion: { _ in
                transitionContext.completeTransition(true)
            }
        }
    }
}

在代理方法中統(tǒng)一傳參

/// 代理方法
extension TempTransitionDelegate: UIViewControllerTransitioningDelegate {
    func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        LogUtil.doPrint("TempTransitionDelegate `animationController` forPresented 被調(diào)用")
        let animate = TempAnimate()
        animate.isPresent = true
        animate.duration = animateDuration
        animate.frame = contentFrame
        return animate
    }
    
    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        LogUtil.doPrint("TempTransitionDelegate `animationController` forDismissed 被調(diào)用")
        let animate = TempAnimate()
        animate.isPresent = false
        animate.duration = animateDuration
        animate.frame = contentFrame
        return animate
    }
    
    func interactionControllerForPresentation(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        LogUtil.doPrint("TempTransitionDelegate `interactionControllerForPresentation` 被調(diào)用")
        return nil
    }
    
    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        LogUtil.doPrint("TempTransitionDelegate `interactionControllerForDismissal` 被調(diào)用")
        return nil
    }
    
    func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
        presented.modalPresentationStyle = .custom
        LogUtil.doPrint("TempTransitionDelegate `presentationController` 被調(diào)用")
        let present = TempPresentation(presentedViewController: presented, presenting: presenting)
        present.duration = animateDuration
        present.frame = contentFrame
        return present
    }
}

大致的效果

動(dòng)畫同步了

同時(shí)放棄了系統(tǒng)從下到上的默認(rèn)彈出效果两疚，而是實(shí)現(xiàn)了從右到左的彈出效果床估，并且速度慢很多含滴。