如何在Swift iOS中注销NSNotification

Question

我有两个控制器

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

        NotificationCenter.default.addObserver(CtrlB.self, selector: #selector(CtrlB.badge(notification:)), name: NSNotification.Name(rawValue: "badge"), object: nil)
    }

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

        NotificationCenter.default.removeObserver(CtrlB.self, name: NSNotification.Name(rawValue: "badge"), object: nil)
    }
}

class CtrlB: UIViewController {
    static func badge (notification: NSNotification) {
        // blah blah
    }
}

注销上面的通知侦听器的正确方法是什么？ 我不确定这是正确的： NotificationCenter.default.removeObserver(CtrlB.self, name: NSNotification.Name(rawValue: "badge"), object: nil)

我也不认为可以使用self ，因为它是在CtrlB.self上CtrlB.self

Answer 1

我不确定为什么要使用类而不是实例来注册/注销通知。 'CtrlB.self'-不会为您提供CtrlB类的实例，实际上它将返回一个类本身。 相反，您应该使用以下内容：

class CtrlA {

    let ctrlBInstance = CtrlB()

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

        NotificationCenter.default.addObserver(ctrlBInstance, selector: #selector(CtrlB.badge(notification:)), name: NSNotification.Name(rawValue: "badge"), object: nil)
    }

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

        NotificationCenter.default.removeObserver(ctrlBInstance, name: NSNotification.Name(rawValue: "badge"), object: nil)
    }
}

在这种情况下，您的ClassB应该看起来像这样：

class CtrlB {
   func badge (notification: NSNotification) {
        // blah blah
    }
}

Answer 2

因此，在项目中实现通知的最佳方法是在内部创建一个称为NotificationManager类，该类声明一本词典，您可以在其中始终更新观察者

class NotificationManager {
var observers = [String: AnyObject]()
}

在同一类中创建addObserver方法，发布通知方法并删除观察者方法。

func postNotification(_ name: String, userInfo: [AnyHashable: Any]? = nil) {
    NotificationCenter.default.post(name: name, object: nil, userInfo: userInfo)
}

func addObserver(_ name: String, block: @escaping (Notification) -> Void) {
 //if observer is already in place for this name, remove it
  removeObserverForName(name)
  let observer = NotificationCenter.default.addObserver(forName: name), object: nil, queue: OperationQueue.main, using: block)
  self.observers[name] = observer
}

func removeObserver(_ name: name) {
 guard let observer = self.observers[name] else { return }
 NotificationCenter.default.removeObserver(observer)
 self.observers.removeValue(forKey: name)
}

 //Removes all observers
func removeAllObservers() {
for observer in self.observers.values {
 NotificationCenter.default.removeObserver(observer)
 }self.observers = [:]
}

因此，在您需要的任何类中访问上述方法，无论需要使用什么方法，它都会处理一切。 这也可以防止代码崩溃。 如果尝试多次删除同一观察者。

Answer 3

您需要获取未声明的观察者实例。

例如，您需要设置类变量secondA ...

class CtrlA: UIViewController {

var secondController: CtrlB?


override func viewDidLoad()
{
super.viewDidLoad()

    if let unwrappedController = storyboard.instantiateViewController(withIdentifier: "someViewController") as? CtrlB
    {
    secondController = unwrappedController        
    }

}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    if let secondController = secondController
    {
    NotificationCenter.default.addObserver(CtrlB.self, selector: #selector(CtrlB.badge(notification:)), name: NSNotification.Name(rawValue: "badge"), object: nil)
    }
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    if let secondController = secondController
    {
    NotificationCenter.default.removeObserver(CtrlB.self, name: NSNotification.Name(rawValue: "badge"), object: nil)
    }
}

//Also don't forget to remove listening on deinit

deinit
{
    if let secondController = secondController
    {
    NotificationCenter.default.removeObserver(secondController, name: NSNotification.Name(rawValue: "badge"), object: nil)
    }
  }
}

    class CtrlB: UIViewController {
        //Here you go with notification...
        static func badge (notification: NSNotification) {
            // blah blah
        }
    }