检测 applicationWillEnterForeground 中存在哪个视图

Question

我想知道当应用程序进入前台时存在哪个视图。

这怎么可能？

func applicationWillEnterForeground(_ application: UIApplication) {

            if (storyboardID == "myview") {

               //do sth

            }

        }

Answer 1

func getCurrentViewController() -> UIViewController? {

      if let rootController = UIApplication.shared.keyWindow?.rootViewController {
      var currentController: UIViewController! = rootController
         while (currentController.presentedViewController != nil) {
                currentController = currentController.presentedViewController
            }
            return currentController
        }
        return nil
    }

使用上面的代码你会得到当前的View Controller。

使用示例

func applicationWillEnterForeground(_ application: UIApplication) {
    if let storyboardID = getCurrentViewController()?.restorationIdentifier, 
           storyboardID == "myview") {
           //do sth
        }
    }

Answer 2

public extension UIWindow {
    public var visibleViewController: UIViewController? {
        return UIWindow.getVisibleViewControllerFrom(self.rootViewController)
    }

    public static func getVisibleViewControllerFrom(_ vc: UIViewController?) -> UIViewController? {
        if let nc = vc as? UINavigationController {
            return UIWindow.getVisibleViewControllerFrom(nc.visibleViewController)
        } else if let tc = vc as? UITabBarController {
            return UIWindow.getVisibleViewControllerFrom(tc.selectedViewController)
        } else {
            if let pvc = vc?.presentedViewController {
                return UIWindow.getVisibleViewControllerFrom(pvc)
            } else {
                return vc
            }
        }
    }
}

Swift 中 UIApplication 的简单扩展（甚至关心 UITabBarController 中的 moreNavigationController：

extension UIApplication {
    class func topViewController(base: UIViewController? = UIApplication.sharedApplication().keyWindow?.rootViewController) -> UIViewController? {

        if let nav = base as? UINavigationController {
            return topViewController(base: nav.visibleViewController)
        }

        if let tab = base as? UITabBarController {
            let moreNavigationController = tab.moreNavigationController

            if let top = moreNavigationController.topViewController where top.view.window != nil {
                return topViewController(top)
            } else if let selected = tab.selectedViewController {
                return topViewController(selected)
            }
        }

        if let presented = base?.presentedViewController {
            return topViewController(base: presented)
        }

        return base
    }
}

简单用法：

   if let rootViewController = UIApplication.topViewController() {
        //do sth with root view controller
    }