尝试显示视图不在窗口层次结构中的vc

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! 

有什么帮助解决这个问题？

Answer 1

在您的应用程序中添加下面的扩展名,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,希望它对您有所帮助.

//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
    }
}

并通过以下代码呈现它:

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