Question

我正在尝试在线程中打开文件，这是我的代码：

DispatchQueue.main.async(execute: { () -> Void in
    var documentsURL = (FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)).appendPathComponent(“File.pdf")
    self.docController = UIDocumentInteractionController.init(url: documentsURL as URL)
    self.docController?.delegate = self as? UIDocumentInteractionControllerDelegate
    self.docController?.presentPreview(animated: true)
    self.docController?.presentOpenInMenu(from: CGRect.zero, in: self.view, animated: true)
})

当移动到主屏幕时，会显示此警告并且文件未打开

Warning: Attempt to present <_UIDocumentActivityViewController: 0x...> on <HCM.PrintVacationDecisionVC: 0x...> whose view is not in the window hierarchy!

有任何帮助解决这个问题吗？

Answer 1

将下面的扩展名添加到您的应用程序中，并在任何您想要呈现任何视图控制器的地方使用它，它对我有用，希望它可以帮助您。

//MARK: - UIApplication Extension
extension UIApplication {
    class func topViewController(viewController: UIViewController? = UIApplication.shared.keyWindow?.rootViewController) -> UIViewController? {
        if let nav = viewController as? UINavigationController {
            return topViewController(viewController: nav.visibleViewController)
        }
        if let tab = viewController as? UITabBarController {
            if let selected = tab.selectedViewController {
                return topViewController(viewController: selected)
            }
        }
        if let presented = viewController?.presentedViewController {
            return topViewController(viewController: presented)
        }
        return viewController
    }
}

通过以下代码呈现它：

 UIApplication.topViewController()?.present(vc, animated: true, completion: nil)

Answer 2

如果您尝试在viewDidLoad方法中显示模态视图控制器，可以尝试将此调用移动到viewDidAppear：方法。

Answer 3

您需要找到顶视图控制器

来自

https://stackoverflow.com/a/26859650/4601900

extension UIViewController {
func topMostViewController() -> UIViewController {
    // Handling Modal views
    if let presentedViewController = self.presentedViewController {
        return presentedViewController.topMostViewController()
    }
    // Handling UIViewController's added as subviews to some other views.
    else {
        for view in self.view.subviews
        {
            // Key property which most of us are unaware of / rarely use.
            if let subViewController = view.nextResponder() {
                if subViewController is UIViewController {
                    let viewController = subViewController as UIViewController
                    return viewController.topMostViewController()
                }
            }
        }
        return self
    }
}
}

extension UITabBarController {
override func topMostViewController() -> UIViewController {
    return self.selectedViewController!.topMostViewController()
}
}

 extension UINavigationController {
override func topMostViewController() -> UIViewController {
    return self.visibleViewController.topMostViewController()
}

}

如何使用

  UIApplication.sharedApplication().keyWindow!.rootViewController!.topMostViewController()

尝试显示视图不在窗口层次结构中的vc

3 个答案: