无限旋转UIView并暂停/停止动画，保持状态，并继续从当前状态旋转

Question

我很难尝试暂停并从任何UIView旋转技术的旋转当前状态继续。

尝试：

CGAffineTransformRotate 
CGAffineTransformMakeRotation 
CATransform3DMakeRotation 
CABasicAnimation 

基本上，如果我叫view.layer.removeAllAnimations()或layer.speed = 0，他们都重置当前旋转度。

此外，还试图快照视图使用图像，而不是真正的旋转，但没有运气，因为快照忽略旋转。

Answer 1

终于得偿所愿，与一个以上的答案上如此，许多在Objective-C，把它们放在一起在UIView的扩展，并将其记录：

extension UIView { 

     /** 
     Will rotate `self` for ever. 

     - Parameter duration: The duration in seconds of a complete rotation (360º). 
     - Parameter clockwise: If false, will rotate counter-clockwise. 
     */ 
     func startRotating(duration duration: Double, clockwise: Bool) { 
      let kAnimationKey = "rotation" 
      var currentState = CGFloat(0) 

      // Get current state 
      if let presentationLayer = layer.presentationLayer(), zValue = presentationLayer.valueForKeyPath("transform.rotation.z"){ 
       currentState = CGFloat(zValue.floatValue) 
      } 

      if self.layer.animationForKey(kAnimationKey) == nil { 
       let animate = CABasicAnimation(keyPath: "transform.rotation") 
       animate.duration = duration 
       animate.repeatCount = Float.infinity 
       animate.fromValue = currentState //Should the value be nil, will start from 0 a.k.a. "the beginning". 
       animate.byValue = clockwise ? Float(M_PI * 2.0) : -Float(M_PI * 2.0) 
       self.layer.addAnimation(animate, forKey: kAnimationKey) 
      } 
     } 

     /// Will stop a `startRotating(duration: _, clockwise: _)` instance. 
     func stopRotating() { 
      let kAnimationKey = "rotation" 
      var currentState = CGFloat(0) 

      // Get current state 
      if let presentationLayer = layer.presentationLayer(), zValue = presentationLayer.valueForKeyPath("transform.rotation.z"){ 
       currentState = CGFloat(zValue.floatValue) 
      } 

      if self.layer.animationForKey(kAnimationKey) != nil { 
       self.layer.removeAnimationForKey(kAnimationKey) 
      } 

      // Leave self as it was when stopped. 
      layer.transform = CATransform3DMakeRotation(currentState, 0, 0, 1) 
     } 

    } 

使用它像yourView.startRotating(duration: 1, clockwise: true)，后来停止做yourView.stopRotating()。