暂停与恢复的UIView动画与Alpha当用户按下Home键不起作用

Question

问：

1. 如何暂停嵌套的UIView动画以动画的α/阻当用户按下主页按钮并返回到应用程序？
2. 我在下面的代码中错过了什么？谢谢。

---

背景：

我有一个简单的嵌套的UIView动画在不同的时间缓慢地调整的图的α从alpha = 0到alpha = 1超过1分钟。

当用户按下主页按钮时，UIView动画不会暂停，因此当应用程序恢复时，UIView动画快进到动画的最后，alpha在恢复应用程序时立即从0变为1 。

所以，我试图暂停UIView动画，当用户按下设备的主页按钮并暂时挂起应用程序。

我有一个函数暂停动画（pauseLayer），然后重新开始动画（resumeLayer）。从UIButton拨打电话时，这两个功能非常有用。它暂停alpha并按预期恢复动画。 （然而，如果被按压主页按钮，而动画暂停时，当它恢复所述α的变化瞬间从0到1）

当我尝试调用pauseLayer当用户按压主页按钮（接收WillResignActive通知），然后返回到应用程序（接收到WillEnterForeground通知），则动画不会暂停并继续，而是在恢复应用程序时alpha会立即从0更改为1。

它似乎应该工作，但事实并非如此。

---

代码：

import UIKit 

class ViewController: UIViewController { 

    @IBOutlet weak var myView1: UIView! 
    @IBOutlet weak var myView2: UIView! 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     setNotifications() 
     myAnimation() 
    } 

    @IBAction func myPauseButton(sender: UIButton) { 
     let layer = self.view.layer 
     pauseLayer(layer) 
    } 

    @IBAction func myResumeButton(sender: UIButton) { 
     let layer = self.view.layer 
     resumeLayer(layer) 
    } 

    func setNotifications() { 
     NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.WillEnterForeground(_:)), name: UIApplicationWillEnterForegroundNotification, object: nil) 

     NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.WillResignActive(_:)), name: UIApplicationWillResignActiveNotification, object: nil) 
    } 

    func WillEnterForeground(notification : NSNotification) { 
     let layer = self.view.layer 
     resumeLayer(layer) 
    } 

    func WillResignActive(notification : NSNotification) { 
     let layer = self.view.layer 
     pauseLayer(layer) 
    } 

    func pauseLayer(layer: CALayer) { 
     let pausedTime: CFTimeInterval = layer.convertTime(CACurrentMediaTime(), fromLayer: nil) 
     layer.speed = 0.0 
     layer.timeOffset = pausedTime 
    } 

    func resumeLayer(layer: CALayer) { 
     let pausedTime: CFTimeInterval = layer.timeOffset 
     layer.speed = 1.0 
     layer.timeOffset = 0.0 
     layer.beginTime = 0.0 
     let timeSincePause: CFTimeInterval = layer.convertTime(CACurrentMediaTime(), fromLayer: nil) - pausedTime 
     layer.beginTime = timeSincePause 
    } 

    func myAnimation() { 
     self.myView1.alpha = 0 
     UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut], animations: { 
      self.myView1.alpha = 0.1 
      }, completion: {(finished: Bool) in 
       UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut], animations: { 
        self.myView1.alpha = 0.2 
        }, completion: {(finished: Bool) in 
         UIView.animateWithDuration(30, delay: 0, options: [.CurveEaseInOut], animations: { 
          self.myView1.alpha = 1 
          }, completion: nil) 
       }) 
     }) 

     self.myView2.alpha = 0 
     UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut], animations: { 
      self.myView2.alpha = 0.1 
      }, completion: {(finished: Bool) in 
       UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut], animations: { 
        self.myView2.alpha = 0.2 
        }, completion: {(finished: Bool) in 
         UIView.animateWithDuration(30, delay: 0, options: [.CurveEaseInOut], animations: { 
          self.myView2.alpha = 1 
          }, completion: nil) 
       }) 
     }) 
    } 

} 

---

编辑：

如果我添加if (finished) {到每个部分，然后按Home键，然后返回到应用程序中，动画只进行到下一个部分并停止，不再进一步。这样比较好，但是问题在于resumeLayer似乎不起作用，所以动画保持停止状态，不会继续。

 self.myView2.alpha = 0 
     UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut, .LayoutSubviews, .AllowUserInteraction, .BeginFromCurrentState], animations: { 
      self.myView2.alpha = 0.1 
      }, completion: {(finished: Bool) in 
       if (finished) { 
       UIView.animateWithDuration(15, delay: 0, options: [.CurveEaseInOut, .LayoutSubviews, .AllowUserInteraction, .BeginFromCurrentState], animations: { 
        self.myView2.alpha = 0.2 
        }, completion: {(finished: Bool) in 
         if (finished) { 
         UIView.animateWithDuration(30, delay: 0, options: [.CurveEaseInOut, .LayoutSubviews, .AllowUserInteraction, .BeginFromCurrentState], animations: { 
          self.myView2.alpha = 1 
          }, completion: nil) 
         } 
       }) 
       } 
     }) 

Answer 1

您不需要使用UIView动画来完成简单的淡入淡出。

您可以使用Timer对象和一些Math来手动设置它。

class ViewController: UIViewController {   
    override func viewDidLoad() { 
     super.viewDidLoad() 
     view.backgroundColor = colorScheme.red 

     NotificationCenter.default.addObserver(self, selector: #selector(self.didBecomeActive), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil) 
     NotificationCenter.default.addObserver(self, selector: #selector(self.didResignActive), name: NSNotification.Name.UIApplicationWillResignActive, object: nil) 
    } 

    func didBecomeActive() { 
     if case min_t..<max_t = t { 
      beginAnimation(at: t) 
     } 
    } 

    func didResignActive() { 
     _ = pauseAnimation() 
    } 


    var t = TimeInterval(0.0) 
    let min_t = TimeInterval(0) 
    let max_t = TimeInterval(100) 
    let delta = TimeInterval(0.1) 
    var timerObj: Timer? 

    func timer(_ aTimer: Timer) { 
     if t < max_t { 
      // Using a parabola 
      view.alpha = CGFloat(0.0001 * t * t) 
     } else { 
      _ = pauseAnimation() 
     } 
     t = t + 1 
    } 

    func beginAnimation(at t: TimeInterval = 0) { 
     self.t = t 
     timerObj = Timer.scheduledTimer(timeInterval: delta, target: self, selector: #selector(self.timer), userInfo: nil, repeats: true) 
    } 

    func pauseAnimation() -> TimeInterval { 
     timerObj?.invalidate() 
     return t 
    } 

    override func viewDidAppear(_ animated: Bool) { 
     beginAnimation() 
    } 
} 

但是，有可能您的应用程序实际上更复杂，您的示例是一个简化。那么，这个怎么样？

class ViewController: UIViewController { 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     view.backgroundColor = .red 

     NotificationCenter.default.addObserver(self, selector: #selector(self.WillEnterForeground(notification:)), name: NSNotification.Name.UIApplicationDidBecomeActive, object: nil) 
     NotificationCenter.default.addObserver(self, selector: #selector(self.WillResignActive(notification:)), name: NSNotification.Name.UIApplicationWillResignActive, object: nil) 
    } 

    func WillEnterForeground(notification : NSNotification) { 
     if let timegap = endDate?.timeIntervalSince(startDate) 
      , timegap < duration { 
      beginAnimation(with: timegap/duration) 
     } 
    } 

    func WillResignActive(notification : NSNotification) { 
     let layer = self.view.layer 
     layer.removeAllAnimations() 
    } 

    var duration = TimeInterval(10) 
    var percentComplete = 0.0 
    var startDate: Date = Date() 
    var endDate: Date? 

    func beginAnimation(with percent: Double = 0.0) { 
     view.alpha = CGFloat(percent) 

     startDate = Date() 
     UIView.animateKeyframes(withDuration: duration * (1 - percent) 
      , delay: 0, options: UIViewKeyframeAnimationOptions.calculationModeLinear, 
       animations: { 
       if percent < 0.2 { 
        UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 0.2, animations: { 
         self.view.alpha = 0.1 
        }) 
       } 
       if percent < 0.5 { 
        UIView.addKeyframe(withRelativeStartTime: 0.2, relativeDuration: 0.3, animations: { 
         self.view.alpha = 0.2 
        }) 
       } 

       UIView.addKeyframe(withRelativeStartTime: 0.5, relativeDuration: 0.7, animations: { 
        self.view.alpha = 1.0 
       }) 
     }) { (b: Bool) in 
      if b == false { 
       self.endDate = Date() 
       if let timegap = self.endDate?.timeIntervalSince(self.startDate) 
        , timegap < self.duration { 
        self.view.alpha = CGFloat(timegap/self.duration) 
       } 
      } 
     } 
    } 

    override func viewDidAppear(_ animated: Bool) { 
     super.viewDidAppear(animated) 
     beginAnimation() 
    } 

} 

主要想法是获取动画开始前的时间和结束时间。如果动画成功，完成会告诉我们，但如果用户按下主页按钮，完成块会告诉我们错误。如果它是错误的，我们可以捕获日期并找出时间差异并计算完成百分比。那么我们可以使用百分比来确定剩下的时间量。

希望帮助