ios - 在UIViewControllerAnimatedTransitioning委托(delegate)中，transitionContext.fromViewController为nil

我有一个UINavigationController设置，希望使用自定义动画来弹出/推送视图。我以前使用过自定义转换，但在本例中，我实际上在“from”和“to”UIViewControllers中找到了零值。
我的设置与此非常相似SO Post
自定义数据入口视图控制器

class DataEntryViewController : UIViewController, DataEntryViewDelegate, UINavigationControllerDelegate {

    func navigationController(navigationController: UINavigationController, animationControllerForOperation operation: UINavigationControllerOperation, fromViewController fromVC: UIViewController, toViewController toVC: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        let animator = DataEntryTransitionAnimator()
        animator.duration = 2
        return animator
    }
}

自定义BaseTrantiationAnimator

class BaseTransitionAnimator : NSObject, UIViewControllerAnimatedTransitioning {

    var duration : NSTimeInterval = 0.5             // default transition time of 1/2 second
    var appearing : Bool = true                     // is the animation appearing (or disappearing)

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

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        assert(true, "animateTransition MUST be implemented by child class")
    }
}

子类传递animator

class DataEntryTransitionAnimator : BaseTransitionAnimator {

    override func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        let containerView = transitionContext.containerView()
        let fromVC = transitionContext.viewControllerForKey(UITransitionContextFromViewKey) as! DataEntryViewController
        let toVC = transitionContext.viewControllerForKey(UITransitionContextToViewKey) as! DataEntryViewController
        let duration = transitionDuration(transitionContext)

        // do fancy animations
    }
}

使用上述方法，fromVC和toVC都为零
transitionContext怎么可能没有指向UIViewControllers的“to”和“from”的有效指针？

最佳答案

您正在使用UITransitionContextFromViewKey，但需要使用UITransitionContextFromViewControllerKey
与“to”相同