Question

我有一种情况，我必须每次从背景到前景初始化一个对象，并且应该使用NSNotificationCenter而不是appdelegate，因为我建立了一个静态库，因此不会有appdelegate，所以请帮助我在同一个。

Answer 1

您是否尝试过UIApplicationWillEnterForegroundNotification？

该应用程序还会在调用applicationWillEnterForeground:之前不久发布UIApplicationWillEnterForegroundNotification通知，以便为感兴趣的对象提供响应转换的机会。

订阅通知：

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(yourUpdateMethodGoesHere:)
                                             name:UIApplicationWillEnterForegroundNotification
                                           object:nil];

实现需要调用的代码：

- (void) yourUpdateMethodGoesHere:(NSNotification *) note {
// code
}

别忘了取消订阅：

[[NSNotificationCenter defaultCenter] removeObserver:self];

Answer 2

Swift 3版本

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    NotificationCenter.default.addObserver(self,
                                           selector:#selector(applicationWillEnterForeground(_:)),
                                           name:NSNotification.Name.UIApplicationWillEnterForeground,
                                           object: nil)
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    NotificationCenter.default.removeObserver(self)
}

func applicationWillEnterForeground(_ notification: NSNotification) {
   ....
}

您也可以使用NSNotification.Name.UIApplicationDidBecomeActive

Answer 3

Swift 4.2

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

Answer 4

Swift 3和4版本

NotificationCenter.default.addObserver(forName: NSNotification.Name.UIApplicationWillEnterForeground, object: nil, queue: nil) { notification in
        ...
}

Answer 5

Swift 5用途： UIApplication.willEnterForegroundNotification

Answer 6

迅速4.1

 override func viewDidAppear(_ animated: Bool) {
        NotificationCenter.default.addObserver(self, selector: #selector(enterForeground), name: Notification.Name.UIApplicationWillEnterForeground, object: nil)
    }

    override func viewDidDisappear(_ animated: Bool) {
        NotificationCenter.default.removeObserver(self, name: Notification.Name.UIApplicationWillEnterForeground, object: nil)
    }

    @objc func enterForeground() {
       // Do stuff
   }

Answer 7

快捷键5

订阅通知-

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

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

删除订阅-

override func viewWillDisappear(_ animated: Bool) {
        super.viewWillDisappear(animated)

        NotificationCenter.default.removeObserver(self)
}

要调用的函数-

@objc func applicationWillEnterForeground(_ notification: NSNotification) {
       self.volumeSlider.value = AVAudioSession.sharedInstance().outputVolume
    }

iOS NSNotificationCenter用于检查应用程序是否从后台到前台

7 个答案:

Swift 4.2