处理applicationDidBecomeActive - "视图控制器如何响应应用程序变为活动状态？"

Question

我UIApplicationDelegate在我的主AppDelegate.m类中有协议,applicationDidBecomeActive定义了方法.

我想在应用程序从后台返回时调用方法,但该方法在另一个视图控制器中.如何检查applicationDidBecomeActive方法中当前显示的视图控制器,然后调用该控制器中的方法？

Answer 1

应用程序中的任何类都可以成为应用程序中不同通知的"观察者".当你创建(或负载)视图控制器,你会希望把它注册作为观察员UIApplicationDidBecomeActiveNotification,并指定你想要的方法时,该通知被发送到你的应用程序来调用.

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(someMethod:)
                                             name:UIApplicationDidBecomeActiveNotification object:nil];

不要忘记自己清理!当您的视图消失时,请记住将自己移除为观察者:

[[NSNotificationCenter defaultCenter] removeObserver:self 
                                                name:UIApplicationDidBecomeActiveNotification
                                              object:nil];

有关通知中心的更多信息.

Answer 2

Swift 3,4等效:

添加观察者

NotificationCenter.default.addObserver(self,
    selector: #selector(applicationDidBecomeActive),
    name: .UIApplicationDidBecomeActive, // UIApplication.didBecomeActiveNotification for swift 4.2+
    object: nil)

删除观察者

NotificationCenter.default.removeObserver(self,
    name: .UIApplicationDidBecomeActive, // UIApplication.didBecomeActiveNotification for swift 4.2+
    object: nil)

打回来

@objc func applicationDidBecomeActive() {
    // handle event
}

Answer 3

Swift 2等效:

let notificationCenter = NSNotificationCenter.defaultCenter()

// Add observer:
notificationCenter.addObserver(self,
  selector:Selector("applicationWillResignActiveNotification"),
  name:UIApplicationWillResignActiveNotification,
  object:nil)

// Remove observer:
notificationCenter.removeObserver(self,
  name:UIApplicationWillResignActiveNotification,
  object:nil)

// Remove all observer for all notifications:
notificationCenter.removeObserver(self)

// Callback:
func applicationWillResignActiveNotification() {
  // Handle application will resign notification event.
}

Answer 4

斯威夫特 5

fileprivate  func addObservers() {
      NotificationCenter.default.addObserver(self,
                                             selector: #selector(applicationDidBecomeActive),
                                             name: UIApplication.didBecomeActiveNotification,
                                             object: nil)
    }

fileprivate  func removeObservers() {
        NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
    }

@objc fileprivate func applicationDidBecomeActive() {
// here do your work
    }

Answer 5

在 Swift 4 中，Apple 通过新的编译器警告提供建议，我们避免#selector在这种情况下使用。以下是实现此目的的更安全的方法：

首先，创建一个可以被通知使用的惰性变量：

lazy var didBecomeActive: (Notification) -> Void = { [weak self] _ in
    // Do stuff
} 

如果您需要实际通知被收录，只需更换_用notification。

接下来，我们设置通知以观察应用程序是否处于活动状态。

func setupObserver() {
    _ = NotificationCenter.default.addObserver(forName: .UIApplicationDidBecomeActive,
                                               object: nil,
                                               queue:.main,
                                               using: didBecomeActive)
}

这里的重大变化是#selector我们现在调用上面创建的 var而不是调用 a 。这可以消除无效选择器崩溃的情况。

最后，我们移除观察者。

func removeObserver() {
    NotificationCenter.default.removeObserver(self, name: .UIApplicationDidBecomeActive, object: nil)
}

Answer 6

斯威夫特4.2

添加观察者-

NotificationCenter.default.addObserver(self, selector: #selector(handleEvent), name: UIApplication.didBecomeActiveNotification, object: nil)

删除观察者-

NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)

处理事件

@objc func handleEvent() {
}

Answer 7

斯威夫特 5版本：

 NotificationCenter.default.addObserver(self,
                                               selector: #selector(loadData),
                                               name: UIApplication.didBecomeActiveNotification,
                                               object: nil)

iOS 9 及更高版本中不再需要删除观察者。

Answer 8

在 Swift 5 中

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

         NotificationCenter.default.addObserver(self, selector: #selector(applicationWillResignActive), name: UIApplication.willResignActiveNotification, object: nil)
    
         NotificationCenter.default.addObserver(self, selector: #selector(applicationDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
        }
    
    override func viewWillDisappear(_ animated: Bool) { 
        super.viewWillDisappear(animated)

        NotificationCenter.default.removeObserver(self, name: UIApplication.willResignActiveNotification, object: nil)

        NotificationCenter.default.removeObserver(self, name: UIApplication.didBecomeActiveNotification, object: nil)
    }


@objc private func applicationWillResignActive() {
    }

    @objc private func applicationDidBecomeActive() {
    }