snapshotView(afterScreenUpdates:true)返回一个空视图 [英] snapshotView(afterScreenUpdates: true) returns an empty view

问题描述

我想为导航控制器实现自定义推送转换.

I want to implement a custom push-transition for a navigation controller.

我首先实现了 UINavigationControllerDelegate ，在其中我返回了 UIViewControllerAnimatedTransitioning 的对象.

I first implemented the UINavigationControllerDelegate where I return an Object of UIViewControllerAnimatedTransitioning.

在这堂课中，我想对目标视图进行快照以对其进行动画处理.但是，对于推送搜索，这是行不通的-快照ist为空.[当我弹出时，我设置了 afterScreenUpdates = false 并且一切正常]

In this class, I want to take a snapshot of the destination view in order to animate it. However, for the push-segue, this doesn't work - the snapshot ist empty. [when I pop back, I set afterScreenUpdates = false and everything works]

    guard let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
        let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) else {
            return
    }

    guard let snapshot = toVC.view.snapshotView(afterScreenUpdates: true) else {
        return }

   // Problem:
   // snapshot is an empty view!

推荐答案

我发现有必要在推送过渡之后和截屏之前引入一小段延迟，例如十分之一秒.避免空白的屏幕截图.可能这会使界面以某种方式稳定下来.

I find that it is necessary to introduce a short delay, say about a tenth of a second, after the push transition and before taking the screenshot, in order to avoid the blank screenshot. Probably this lets the interface settle down in some way.

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