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

Question

我有一种情况，每次从后台到前台时我都必须初始化一个对象，并且应该使用 NSNotificationCenter 而不是 appdelegate 因为我正在构建一个静态库所以不会有 appdelegate 所以请帮助我同样。

Answer 1

斯威夫特 5

 override func viewDidAppear(_ animated: Bool) {
    NotificationCenter.default.addObserver(self, selector: #selector(appMovedToForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
    }
    
    override func viewDidDisappear(_ animated: Bool) {
    NotificationCenter.default.removeObserver(self, name: NSNotification.Name(rawValue: UIApplication.willEnterForegroundNotification.rawValue), object: nil)
    }

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

Answer 2

Swift 5 使用： UIApplication.willEnterForegroundNotification

Answer 3

斯威夫特 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
    }

Answer 4

斯威夫特 4.2

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

Answer 5

Swift 3 和 4 版本

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

Answer 6

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) {
   ....
}

你也可以使用NSNotification.Name.UIApplicationDidBecomeActive

Answer 7

你试过UIApplicationWillEnterForegroundNotification吗？

该应用还在调用 applicationWillEnterForeground: 之前不久发布 UIApplicationWillEnterForegroundNotification 通知，让感兴趣的对象有机会响应转换。

订阅通知：

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

实现一个需要调用的代码：

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

别忘了退订：

[[NSNotificationCenter defaultCenter] removeObserver:self];