Question

我正在为我的应用创建自定义转换，但是当我尝试创建目标视图的快照时，它始终显示为空白的白色矩形。重要的是我注意到这是一个自定义push转换，而不是视图的模态表示。以模态方式呈现快照似乎有效。这是自定义push / pop转换的正常行为吗？

我写的代码如下：

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    guard let toViewController = transitionContext.viewController(forKey: .to) as? CultureViewController else {
        return
    }

    let containerView = transitionContext.containerView
    let finalFrame = transitionContext.finalFrame(for: toViewController)

    let snapshot = toViewController.view.snapshotView(afterScreenUpdates: true)
    snapshot?.frame = UIScreen.main.bounds
    containerView.addSubview(snapshot!)

    toViewController.view.transform = CGAffineTransform(translationX: 0, y: toViewController.view.bounds.height)
    //containerView.addSubview(toViewController.view)

    let duration = transitionDuration(using: transitionContext)
    UIView.animateKeyframes(withDuration: duration, delay: 0, options: .calculationModeCubic, animations: { 
        UIView.addKeyframe(withRelativeStartTime: 0, relativeDuration: 1, animations: { 
            toViewController.view.frame = finalFrame
        })
    }, completion: { _ in
        transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    })
}

Answer 1

在呈现视图之前拍摄视图的快照，例如在调用containerView.addSubview(toViewController.view)之前转换的情况，按UIView's documentation返回空白视图。

如果当前视图尚未呈现，可能是因为它尚未在屏幕上显示，则快照视图没有可见内容。

自定义UIViewController转换的UIView快照

1 个答案: