Question

我有一个UITabBar控制器作为主控制器，带有2个标签。每个标签都是嵌入了NavigatorViewController的{{1}}。

如果在上次冷启动后从后台打开应用程序，则不会触发UIViewController（ViewWillAppear，UITabBarController）。

当用户来自backgroud时，如何调用UITabBarChildren的生命周期？（即：从通知中获取）

Answer 1

那不是生命周期，因为在后台模式或其他应用程序事件期间控制器的状态没有改变。

您应该注意applicationWillEnterForegroundNotification

class VC: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        // Listen for application event somewhere early like `ViewDidLoad`
        NotificationCenter.default.addObserver(self, selector: #selector(applicationWillEnterForegroundNotification), name: UIApplication.willEnterForegroundNotification, object: nil)
    }

    // Implement a function that you want to execute when event happen
    @objc func applicationWillEnterForegroundNotification() {
        // Do anything before application Enter Foreground
    }

    // Remove observer when the controller is going to remove to prevent further issues
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

Answer 2

当应用程序来自非活动vc的非后台调用viewWillAppear/viewDidAppear时，您需要像applicationWillEnterForegroundNotification那样监听应用程序委托

NotificationCenter.default.addObserver(self, selector: #selector(applicationWillEnterForegroundNotification), name: UIApplication.willEnterForegroundNotification, object: nil)

@objc func applicationWillEnterForegroundNotification(_ notification: NSNotification) {
  print("To-Do")
}

Answer 3

您可以在observer的 UIApplicationWillEnterForeground 中添加一个controllers。

在应用离开背景状态之前不久发布成为活动应用。

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self,selector: #selector(self.appEnteredFromBackground(_:)),name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
}

@objc func appEnteredFromBackground(_ notification: NSNotification) {
    print("From background")
}

UITabBar Lifecycle的方法未从后台启动

3 个答案: