看过iOS动画之旅的都知道,其中在最后提到一个作者写的开源动画库EasyAnimation(以下简称EA).

EA对CoreAnimation中的view和layer动画做了更高层次的包装和抽象,使得我们可以大大减少编写代码的行数.

不过在玩耍EA时发现了点小问题,在使用链式串行调用中其中的某一段若为弹簧动画,则该动画后面的其他动画都无法再运行了.

以下是测试代码:

@IBAction func actionAddItem(sender: AnyObject) {

    plusButton.enabled = false

    UIView.animateAndChainWithDuration(1.0, delay: 0.0, usingSpringWithDamping: 0.33, initialSpringVelocity: 0.0, options: [], animations: {
            //1
            self.plusButton.transform = CGAffineTransformRotate(self.plusButton.transform, CGFloat(-M_PI_2))

        }, completion: {_ in
            self.addRandomItem()
    }).animateWithDuration(1.0, delay: 0.0, usingSpringWithDamping: 0.33, initialSpringVelocity: 0.0, options: [], animations: {
        //2
        self.plusButton.layer.cornerRadius = 62.5
        self.plusButton.layer.borderWidth = 2.0
        self.plusButton.layer.borderColor = UIColor.grayColor().CGColor
        }, completion: nil).animateWithDuration(0.15, delay: 0.5, options: [.CurveEaseOut,/*.Repeat*/], animations: {
                //3
                self.plusButton.layer.cornerRadius = 0.0
                self.plusButton.layer.borderWidth = 0.0
                self.plusButton.layer.borderColor = UIColor.clearColor().CGColor

            }, completion: {_ in
                self.plusButton.enabled = true
        })

  }

以上我们总共串行执行了3段动画,上面数字注释分别依次指明当前的动画段.

在第一段中我们旋转按钮,在第二段动画中我们修改按钮的边角,边线的样式,在最后一段中我们恢复第二段中做的样式修改.

注意第二段中我们使用了弹簧动画,执行App你会发现第三段动画无法被触发!

cmd+鼠标左键点击第二段中的弹簧动画,我们看一下EA源代码:

public func animateWithDuration(duration: NSTimeInterval, delay: NSTimeInterval, usingSpringWithDamping dampingRatio: CGFloat, initialSpringVelocity velocity: CGFloat, options: UIViewAnimationOptions, animations: () -> Void, completion: ((Bool) -> Void)?) -> EAAnimationDelayed {
        let anim = animateAndChainWithDuration(duration, delay: delay, options: options, animations: animations, completion: completion)
        self.springDamping = dampingRatio
        self.springVelocity = velocity
        return anim
    }

其中返回了另一个EAAnimationDelayed对象,我们再看一下animateAndChainWithDuration这个方法:

public func animateAndChainWithDuration(duration: NSTimeInterval, delay: NSTimeInterval, options: UIViewAnimationOptions, animations: () -> Void, completion: ((Bool) -> Void)?) -> EAAnimationDelayed {
        var options = options

        if options.contains(.Repeat) {
            options.remove(.Repeat)
            loopsChain = true
        }

        self.duration = duration
        self.delay = delay
        self.options = options
        self.animations = animations
        self.completion = completion

        nextDelayedAnimation = EAAnimationDelayed()
        nextDelayedAnimation!.prevDelayedAnimation = self
        return nextDelayedAnimation!
    }

如你所见,该方法只是简单的把CoreAnimation动画中的一些参数放到EAAnimationDelayed对象中来,同时很重要的一步是在方法最后建立EAAnimationDelayed执行链.

我们最后看一下执行链是如何执行的,看一下run方法:

func run() {
        if debug {
            print("run animation #\(debugNumber)")
        }
        //TODO: Check if layer-only animations fire a proper completion block
        if let animations = animations {
            options.insert(.BeginFromCurrentState)
            let animationDelay = dispatch_time(DISPATCH_TIME_NOW, Int64( Double(NSEC_PER_SEC) * self.delay ))

            dispatch_after(animationDelay, dispatch_get_main_queue()) {
                if self.springDamping > 0.0 {
                    //spring animation
                    UIView.animateWithDuration(self.duration, delay: 0, usingSpringWithDamping: self.springDamping, initialSpringVelocity: self.springVelocity, options: self.options, animations: animations, completion: self.animationCompleted)
                } else {
                    //basic animation
                    UIView.animateWithDuration(self.duration, delay: 0, options: self.options, animations: animations, completion: self.animationCompleted)
                }
            }
        }
    }

注意,其中根据springDaming属性的值决定调用何种动画方法!但是在前面EA的animateWithDuration方法中我们赋值的是self的属性,而不是anim的属性!

将EA源代码中上面两句赋值语句修改如下:

anim.springDamping = dampingRatio
anim.springVelocity = velocity

再次运行,可以看到恢复动画可以正常运行了:]