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关于ios:轻量化的iOS动画框架实现

本文作者:有恒

一、背景

日常开发过程中,常常须要对视图做动画,如果须要对一个 view 进行动画操作:3s 淡入,完结后,1s 放大,很容易写出这样的代码:

UIView.animate(withDuration: 3, animations: {view.alpha = 1}, completion: { _ in
    UIView.animate(withDuration: 1) {view.frame.size = CGSize(width: 200, height: 200)
    }
})

如果,是更多串行的动画须要实现呢?

UIView.animate(withDuration: 3, animations: {......}, completion: { _ in
    UIView.animate(withDuration: 3) {......}, completion: { _ in 
          UIView.animate(withDuration: 3) {......}, completion: { _ in 
                  ......
                }
    }
})

这样的回调天堂代码,很难保护也不优雅。

业界也有一些现成的动画库,比拟出名的有:

  • Spring: 轻量级的、基于 Swift 实现的动画库,它提供了多种弹簧成果动画成果。毛病是性能绝对较少,不能满足所有的动画需要。
  • Hero:一个高度可定制化的 iOS 动画库,它反对多种动画成果,如过渡动画、视图转场等。毛病是对于简单的动画成果可能须要编写大量的代码。
  • TweenKit:一个轻量级的、基于 Swift 实现的动画库,它提供了多种动画成果,如突变成果、旋转成果等。TweenKit 的长处是易于应用,对于入门级的开发者很敌对,但毛病是性能绝对较少,不能满足所有的动画需要。

以上动画库各有长处和毛病,总的来说都有书写绝对简单不够优雅的缺点,那有没有不便开发和保护的代码格局?

动画串行执行:

view.at.animate(.fadeIn(duration: 3.0),
   .scale(toValue: 1.2, duration: 0.5)
)

动画并行执行:

view.at.animate(parallelism:
        .fadeIn(duration: 3.0),
        .scale(toValue: 1.2, duration: 1)
)

如果是多个视图组合动画串行执行呢?

AT.animate (
    view1.at.animate(parallelism:
        .fadeIn(duration: 3.0),
        .scale(toValue: 1.2, duration: 1)
    )
      view2.at.animate(parallelism:
        .fadeIn(duration: 3.0),
        .scale(toValue: 1.2, duration: 1)
        )
)

二、实现计划

Animator

动画执行器

public protocol Animator {
    associatedtype T
    mutating func start(with view : UIView)
    func pause()
    func resume()
    func stop()}

封装 UIViewPropertyAnimator,CAKeyframeAnimator,CABasicAnimator,遵循 Animator 协定,实现不同类型的动画执行器。

Animation

Animation 提供动画执行参数:

为不同的 Animator 制订不同的 Animation 协定:

public protocol AnimationBaseProtocol {var duration : TimeInterval { get}
}

protocol CAAnimationProtocol : AnimationBaseProtocol {var repeatCount : Float { get}
    var isRemovedOnCompletion : Bool {get}
    var keyPath : String? {get}
    var animationkey : String? {get}
}

protocol ProPertyAnimationProtocol : AnimationBaseProtocol {var curve : UIView.AnimationCurve { get}
    var fireAfterDelay : TimeInterval {get}
    var closure : (UIView) -> Void {get}
}

protocol CABaseAnimationProtocol: CAAnimationProtocol {var fromValue: Any { get}
    var toValue : Any {get}
}

protocol CAKeyFrameAnimationProtocol: CAAnimationProtocol {var keyTimes: [NSNumber]? {get}
    var timingFunction: CAMediaTimingFunction? {get}
    var valuesClosure: ((UIView) -> [Any]?) {get}
}

须要留神的是,动画执行器反对多种实现,用到了范型,动画执行器作为返回值,应用时须要对其进行类型擦除。

类型擦除

类型擦除的作用是擦除范型的具体信息,以便在运行时应用:

定义一个范型类:

class Stack<T> {var items = [T]()
    
    func push(item: T) {items.append(item)
    }
    
    func pop() -> T? {
        if items.isEmpty {return nil} else {return items.removeLast()
        }
    }
}

如果这样应用:

// 实例化一个 Stack<String> 对象
        let stackOfString = Stack<String>()
        stackOfString.push(item: "hello")
        stackOfString.push(item: "world")

        // 实例化一个 Stack<Int> 对象
        let stackOfInt = Stack<Int>()
        stackOfInt.push(item: 1)
        stackOfInt.push(item: 2)
        
        let stackArray: [Stack] = [stackOfString, stackOfInt]

会有一个谬误:

因为这是两种类型。

如何进行擦除?

class AnyStack {private let pushImpl: (_ item: Any) -> Void
    private let popImpl: () -> Any?
    
    init<T>(_ stack: Stack<T>) {
        pushImpl = { item in
            if let item = item as? T {stack.push(item: item)
            }
        }
        popImpl = {return stack.pop()
        }
    }
    
    func push(item: Any) {pushImpl(item)
    }
    
    func pop() -> Any? {return popImpl()
    }
}

这样执行上面代码就能够失常编译应用:

let stackArray: [AnyStack] = [AnyStack(stackOfString), AnyStack(stackOfInt)]

回到 Animator 的设计,同样的原理,这样就解决了形参类型不统一的问题。

具体实现
extension Animator {public static func fadeIn(duration: TimeInterval = 0.25, curve:UIView.AnimationCurve = .linear , fireAfterDelay: TimeInterval = 0.0, completion:(()-> Void)? = nil) -> AnyAnimator<Animation> {let propertyAnimation = PropertyAnimation()
        propertyAnimation.duration = duration
        propertyAnimation.curve = curve
        propertyAnimation.fireAfterDelay = fireAfterDelay
        propertyAnimation.closure = {$0.alpha = 1}
        return Self.creatAnimator(with: propertyAnimation,completion: completion)
    }
  
  public static func scale(valus: [NSNumber], keyTimes: [NSNumber], repeatCount: Float = 1.0, duration: TimeInterval = 0.3, completion:(()-> Void)? = nil) -> AnyAnimator<Animation> {let animation = CAFrameKeyAnimation()
        animation.keyTimes = keyTimes
        animation.timingFunction = CAMediaTimingFunction(name: .linear)
        animation.valuesClosure = {_ in valus}
        animation.repeatCount = repeatCount
        animation.isRemovedOnCompletion = true
        animation.fillMode = .removed
        animation.keyPath = "transform.scale"
        animation.animationkey = "com.moyi.animation.scale.times"
        animation.duration = duration
        return AnyAnimator.init(CAKeyFrameAnimator(animation: animation,completion: completion))
    }
  
  /// 自定义 Animation
  public static func creatAnimator(with propertyAnimation : PropertyAnimation, completion:(()-> Void)? = nil) -> AnyAnimator<Animation> {return AnyAnimator.init(ViewPropertyAnimator(animation:propertyAnimation,completion:completion))
      }
}
    

CAAnimation 是 Core Animation 框架中负责动画成果的类,它定义了一系列动画成果相干的属性和办法。能够通过创立 CAAnimation 的子类,如 CABasicAnimation、CAKeyframeAnimation、CAAnimationGroup 等来实现不同类型的动画成果。

其中,keypath 是 CAAnimation 的一个重要概念,用于指定动画成果所作用的属性。keypath 的值通常为字符串类型,在指定属性时须要应用 KVC(键值编码)来进行拜访。

更多对于 CAAnimation 的内容能够参考援用中相干链接,不是本文重点不再开展。

AnimationToken

AnimationToken 是视图和动画执行器的封装,用于视图的动画解决。

而后对 UIView 增加串行、并行的扩大办法:

extension EntityWrapper where This: UIView {internal func performAnimations<T>(_ animators: [AnyAnimator<T>] , completionHandlers: [(() -> Void)]) {
        guard !animators.isEmpty else {
            completionHandlers.forEach({ handler in
                handler()})
            return
        }
        
        var leftAnimations = animators
        var anyAnimator = leftAnimations.removeFirst()
        
        anyAnimator.start(with: this)
        anyAnimator.append {self.performAnimations(leftAnimations, completionHandlers: completionHandlers)
        }
    }
    
    internal func performAnimationsParallelism<T>(_ animators: [AnyAnimator<T>], completionHandlers: [(() -> Void)]) {
        guard !animators.isEmpty else {
            completionHandlers.forEach({ handler in
                handler()})
            return
        }
        
        let animationCount = animators.count
        var completionCount = 0
        
        let animationCompletionHandler = {
            completionCount += 1
            if completionCount == animationCount {
                completionHandlers.forEach({ handler in
                    handler()})
            }
        }

        for var animator in animators {animator.start(with: this)
            animator.append {animationCompletionHandler()
            }
        }
    }
}

completionHandlers 是动画工作的完结的回调逻辑,相似 UIView 类办法 animate 的 completion 回调,这样就有了动画完结的回调能力。

给 UIView 增加扩大,实现 view.at.animate () 办法:

extension EntityWrapper where This: UIView {@discardableResult private func animate<T>(_ animators: [AnyAnimator<T>]) -> AnimationToken<T> {
        return AnimationToken(
            view: this,
            animators: animators,
            mode: .inSequence
        )
    }

    @discardableResult public func animate<T>(_ animators: AnyAnimator<T>...) -> AnimationToken<T> {return animate(animators)
    }

    @discardableResult private func animate<T>(parallelism animators: [AnyAnimator<T>]) -> AnimationToken<T> {
        return AnimationToken(
            view: this,
            animators: animators,
            mode: .parallelism
        )
    }

    @discardableResult public func animate<T>(parallelism animators: AnyAnimator<T>...) -> AnimationToken<T> {return animate(parallelism: animators)
    }
}

AT.animate () 对 AnimationToken 进行串行治理,不再赘述。

三、总结

本文只是对动画回调嵌套问题的轻量化解决方案,让组合动画的代码构造更加清晰,不便开发和后续迭代批改。实现计划还有许多能够改良的中央,欢送参考斧正。

四、参考资料

  1. 图源:https://unsplash.com/photos/PDxp-AItBMA
  2. [Declarative animation]https://www.swiftbysundell.com/articles/building-a-declarativ…
  3. [CAAnimation] Apple Inc. Core Animation Programming Guide. [About Core Animation](About Core Animation)
  4. [CAAnimation] 王巍. iOS 动画高级技巧 [M]. 北京:人民邮电出版社,2015.
  5. [CAAnimation]https://developer.apple.com/documentation/quartzcore/caanimat…
  6. [CAAnimation]https://github.com/pro648/tips/blob/master/sources/CAAnimation%EF%BC%9A%E5%B1%9E%E6%80%A7%E5%8A%A8%E7%94%BBCABasicAnimation%E3%80%81CAKeyframeAnimation%E4%BB%A5%E5%8F%8A%E8%BF%87%E6%B8%A1%E5%8A%A8%E7%94%BB%E3%80%81%E5%8A%A8%E7%94%BB%E7%BB%84.md
  7. [UIViewPropertyAnimator]https://developer.apple.com/documentation/uikit/uiviewpropert…
  8. [应用 UIViewPropertyAnimator 做动画]https://swift.gg/2017/04/20/quick-guide-animations-with-uivie…

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