segueForUnwindingToViewController 导致 "Warning: Attempt to present <...> on <...> which is already presenting <...>"

Question

我正在构建一个应用程序，最近发现了由传统 segues 引起的巨大内存泄漏。因此我了解了 unwind segue。如果我简单地使用：

一切正常

    @IBAction func prepareForUnwindToMainFromFriends(segue: UIStoryboardSegue) {
    }

内存泄漏已解决 'everything is awesome'。但是从 UI 的角度来看，这个解决方案看起来很丑陋。所以我从this website实现了这个功能。并且稍微改了一下。

override func segueForUnwindingToViewController(toViewController: UIViewController, fromViewController: UIViewController, identifier: String?) -> UIStoryboardSegue {
    return UIStoryboardSegue(identifier: identifier, source: fromViewController, destination: toViewController) {
        let fromView = fromViewController.view
        let toView = toViewController.view
        if let containerView = fromView.superview {
            let initialFrame = fromView.frame
            var offscreenRect = initialFrame
            var offscreenRectFinal = initialFrame
            offscreenRect.origin.x += CGRectGetWidth(initialFrame)
            offscreenRectFinal.origin.x -= CGRectGetWidth(initialFrame)
            toView.frame = offscreenRect
            containerView.addSubview(toView)
            let duration: NSTimeInterval = 1.0
            let delay: NSTimeInterval = 0.0
            let options = UIViewAnimationOptions.CurveEaseInOut
            let damping: CGFloat = 0.9
            let velocity: CGFloat = 4.0
            UIView.animateWithDuration(duration, delay: delay, usingSpringWithDamping: damping,
                initialSpringVelocity: velocity, options: options, animations: {
                    toView.frame = initialFrame
                    fromView.frame = offscreenRectFinal
                    
                }, completion: { finished in
                    fromView.removeFromSuperview()
                    if let navController = toViewController.navigationController {
                        navController.popToViewController(toViewController, animated: false)
                    }
            })
        }
    }
}

但现在我收到一条错误消息：

2015-05-12 08:47:31.841 PING0.4[4343:1308313] Warning: Attempt to present <NotificationViewController: 0x177030b0>  on <PING0_4.ViewController: 0x16271000> which is already presenting <NotificationViewController: 0x1a488170>

我的应用被屏蔽了。我可以从 VC1 转到 VC2，然后回到 VC2，但之后我就不能再回到 VC1。这个segue我好像只能用一次

有人知道发生了什么事吗？

Answer 1

使用上述过渡动画代码创建了展开转场的示例代码。查看 SampleUnwind 项目，这将帮助您了解 unwind segue（以及它是多么简单）。

项目中有一个导航控制器，里面有三个视图控制器（Home->First->second）。

在 Home 控制器中创建以下展开操作，当点击第二个控制器的 'Home' 按钮时将调用该操作（简单的展开操作）。

@IBAction func unwindToHomeViewController(segue:UIStoryboardSegue) {
}

我创建了 TempNavigationController 子类 UINavigationController 并将其 TempNavigationController 设置为情节提要中的导航控制器。您给出的上述方法在其中存在，因为根据以下参考，这将是 fromViewController 的容器。

参考：Apple 关于在两个子视图控制器之间转换的文档。

您可以将其与您的项目进行比较，也许您可以在您的项目中找到任何重复的（或 multiple/wrong）segue。

segueForUnwindingToViewController 导致 "Warning: Attempt to present <...> on <...> which is already presenting <...>"

segueForUnwindingToViewController causing "Warning: Attempt to present <...> on <...> which is already presenting <...>"

ios

segue

uistoryboardsegue

swift

unwind-segue