swift – 为UIViewPropertyAnimator的fractionComplete设置动画

animator = UIViewPropertyAnimator(duration: 1,curve: .linear) {
        self.blurEffectView.effect = nil
    }

animator?.fractionComplete = blurValue

似乎fractionComplete有一个bug(我在Stackoverflow上的问题： UIViewPropertyAnimator does not update the view when expected),rdar://30856746.该属性只将状态从非活动状态设置为活动状态,但不更新视图,因为(我假设)还有另一个内部状态不会触发.

要解决此问题,您可以执行以下操作：

animator.startAnimation() // This will change the `state` from inactive to active
animator.pauseAnimation() // This will change `isRunning` back to false,but the `state` will remain as active

// Now any call of `fractionComplete` should update your view correctly!
animator.fractionComplete = /* your value here */

这是一个可以玩的游乐场片段：

let liveView = UIView(frame: CGRect(x: 0,y: 0,width: 400,height: 50))
liveView.backgroundColor = .white

PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = liveView

let square = UIView(frame: CGRect(x: 0,width: 50,height: 50))
square.backgroundColor = .red

liveView.addSubview(square)

let animator = UIViewPropertyAnimator.init(duration: 5,curve: .linear)

animator.addAnimations {

    square.frame.origin.x = 350
}

let blurView = UIVisualEffectView(effect: UIBlurEffect(style: .dark))
blurView.frame = liveView.bounds

liveView.addSubview(blurView)

animator.addAnimations {

    blurView.effect = nil
}

// If you want to restore the blur after it was animated,you have to 
// safe a reference to the effect which is manipulated
let effect = blurView.effect

animator.addCompletion {
    // In case you want to restore the blur effect
    if $0 == .start { blurView.effect = effect }
}

animator.startAnimation()
animator.pauseAnimation()

DispatchQueue.main.asyncAfter(deadline: .now() + 2) {

    animator.fractionComplete = 0.5
}

DispatchQueue.main.asyncAfter(deadline: .now() + 4) {

    // decide the direction you want your animation to go.
    // animator.isReversed = true
    animator.startAnimation()
}