ios-UIView.animateWithDuration的交互式转换完成块从未在animateTransition内部调用

Question

我将自定义交互式弹出过渡与平移手势识别器一起使用。我有UIPercentDrivenInteractiveTransition的子类来处理用户操作：

class InteractiveTransitionManager: UIPercentDrivenInteractiveTransition {

  var viewController: UIViewController?
  var interactive: Bool = false

  var popInProgress = false
  var startX: CGFloat = 0

  init(viewController: UIViewController) {
    super.init()
    self.viewController = viewController
    self.viewController?.view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: "handlePan:"))
  }

  func handlePan(pan: UIPanGestureRecognizer) {
    if pan.velocityInView(pan.view!.superview!).x > 0 && !popInProgress {
      popInProgress = true
      interactive = true
      startX = pan.locationInView(pan.view!.superview!).x
      viewController?.navigationController?.popViewControllerAnimated(true)
      return
    }
    let curX = pan.locationInView(pan.view!.superview!).x
    let progress: CGFloat = max(0, curX - startX) / pan.view!.frame.width
    if pan.state == .Changed {
      updateInteractiveTransition(progress)
    } else if pan.state == .Ended || pan.state == .Cancelled {
      if progress > 0.5 {
        finishInteractiveTransition()
      } else {
        cancelInteractiveTransition()
      }
      popInProgress = false
      interactive = false
    }
  }

}

而且我有用于过渡动画的InteractivePopTr​​ansition类：

class InteractivePopTransition: NSObject, UIViewControllerAnimatedTransitioning {

func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
    return 0.3
}

func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
    let fromVC = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey)!
    let toVC = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey)!
    let fromView = transitionContext.viewForKey(UITransitionContextFromViewKey)!
    let toView = transitionContext.viewForKey(UITransitionContextToViewKey)!
    let containterView = transitionContext.containerView()

    let targetFrame = transitionContext.finalFrameForViewController(toVC)

    toView.frame = CGRect(x: -targetFrame.size.width, y: targetFrame.origin.y, width: targetFrame.width, height: targetFrame.height)
    containterView?.insertSubview(toView, belowSubview: fromView)

    UIView.animateWithDuration(transitionDuration(transitionContext), animations: {
        toView.frame = targetFrame
        fromView.frame.origin.x = CGRectGetMaxX(targetFrame)
        }, completion: { b in
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled())
    })
}

}

我有一个问题，有时UIView.animateWithDuration中的完成块没有被调用。为什么会发生这种情况以及如何解决？

Answer 1

[当调用animateTransition(transitionContext:)且用户交互不是交互式的（如程序动画触发器）时，系统似乎存在计时问题，并且未调用UIView.animateWithDuration的completion，如您所描述的。

我在工作中体会到了这一点，通过在调用finishInteractiveTransition之前从UIPercentDrivenInteractiveTransition内部显式调用animateTransition(transitionContext:)对象上的UIView.animateWithDuration(...)，能够解决此问题。

对于我的情况，这是一个简单的解决方案，因为我的UIViewControllerAnimatedTransitioning对象具有UIPercentDrivenInteractiveTransition子类的实例，并且我公开了interactionInProgress属性来确定何时应显式调用finishInteractiveTransition。

如果您在交互式转换对象上显式调用finishInteractiveTransition，则将调用完成块。

class InteractivePopTransition: NSObject, UIViewControllerAnimatedTransitioning {
  private var interactiveTransitionManager: InteractiveTransitionManager
  ...
  func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
    ...
    if !interactiveTransitionManager.isInProgress {
      // Weird state where system is telling you to animate a transition, but there
      // is no interactive transition occurring. Manually finish the non-existant
      // interactive transition so system will call other animation callbacks
      // appropriately to complete the entire transition
      interactiveTransitionManager.finish()
    }
    UIView.animateWithDuration(...)
  }  
}

另一种解决方案是将UIView.animateWithDuration放在具有较小延迟的调度异步块中。