Question

我想实现一个单独的ErrorHandler类，它会在某些事件上显示错误消息。应该从不同的其他类调用此类的行为。发生错误时，它将输出UIAlertView。此AlertView的显示应始终位于顶部。因此无论从何处抛出Error，最顶层的viewController都应该显示AlertMessage（例如，当异步后台进程失败时，我想要一条错误消息，无论前景中显示什么视图）。

我找到了几个似乎可以解决我的问题的要点（见下面的代码）。但是调用UIApplication.sharedApplication().keyWindow?.visibleViewController()会返回一个零值。

从gist扩展

extension UIWindow {
func visibleViewController() -> UIViewController? {
if let rootViewController: UIViewController  = self.rootViewController {
  return UIWindow.getVisibleViewControllerFrom(rootViewController)
}
return nil
}

class func getVisibleViewControllerFrom(vc:UIViewController) -> UIViewController {

if vc.isKindOfClass(UINavigationController.self) {

  let navigationController = vc as! UINavigationController
  return UIWindow.getVisibleViewControllerFrom( navigationController.visibleViewController)

} else if vc.isKindOfClass(UITabBarController.self) {

  let tabBarController = vc as! UITabBarController
  return UIWindow.getVisibleViewControllerFrom(tabBarController.selectedViewController!)

} else {

  if let presentedViewController = vc.presentedViewController {

    return UIWindow.getVisibleViewControllerFrom(presentedViewController.presentedViewController!)

  } else {

    return vc;
  }
}
}
}

Answer 1

Amit89为解决方案带来了一条道路。您必须调用AppDelegate的.window属性。所以我从下面的链接更改了Swift代码，以便找到最顶层的ViewController。确保视图已在视图层次结构中。因此，无法从.viewDidLoad

调用此方法

查找最顶层ViewController *

的扩展程序

extension UIApplication {
  class func topViewController(base: UIViewController? = (UIApplication.sharedApplication().delegate as! AppDelegate).window?.rootViewController) -> UIViewController? {
    if let nav = base as? UINavigationController {
      return topViewController(base: nav.visibleViewController)
    }
    if let tab = base as? UITabBarController {
      if let selected = tab.selectedViewController {
        return topViewController(base: selected)
      }
    }
    if let presented = base?.presentedViewController {
      return topViewController(base: presented)
    }
    return base
  }
}

此代码源自Yonat中的GitHub用户comment到ObjectiveC等效项。我只更改了代码位，使其无法使用.keyWindow属性

Answer 2

你是否从同一个链接尝试过这个？

let appDelegate = UIApplication.sharedApplication().delegate as! MYAppDelegate//Your app delegate class name.


extension UIApplication {
    class func topViewController(base: UIViewController? = appDelegate.window!.rootViewController) -> UIViewController? {
        if let nav = base as? UINavigationController {
            return topViewController(base: nav.visibleViewController)
        }
        if let tab = base as? UITabBarController {
            if let selected = tab.selectedViewController {
                return topViewController(base: selected)
            }
        }
        if let presented = base?.presentedViewController {
            return topViewController(base: presented)
        }
        return base
    }
}

在iOS Swift中获取顶级ViewController

2 个答案: