在 UIViewControllerAnimatedTransitioning 委托中，transitionContext.fromViewController 为 nil

Posted 2023-03-10

【中文标题】在 UIViewControllerAnimatedTransitioning 委托中，transitionContext.fromViewController 为 nil

【英文标题】：Inside UIViewControllerAnimatedTransitioning delegate, the transitionContext.fromViewController is nil

【发布时间】：2016-05-20 18:19:26

【问题描述】：

我有一个 UINavigationController 设置，并希望使用自定义动画来弹出/推送视图。我之前使用过自定义转换没有问题，但在这种情况下，我实际上在我的“from”和“to”UIViewControllers中找到了 nil 值。

我的设置与SO Post非常相似

自定义 DataEntryViewController

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 BaseTransitionAnimator

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TransitionAnimator

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 'to' 和 'from' UIViewControllers 的有效指针？

【参考方案1】：

您正在使用UITransitionContextFromViewKey，但您需要使用UITransitionContextFromViewControllerKey

“到”也一样

【讨论】：

:facepalm: 哈，谢谢。我在命令行上调试并且也在查看调试窗口，发誓它对 VC 显示为 nil，但可能是由于可选的，它看起来很有趣。还在习惯 Swift。

别担心！简单的错字，很容易漏掉。 ?