Swift使協議擴展成為通知觀察者

Question

我們考慮以下代碼：

protocol A {
    func doA()
}

extension A {
  func registerForNotification() {
      NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardDidShow:"), name: UIKeyboardDidShowNotification, object: nil)
  }

  func keyboardDidShow(notification: NSNotification) {

  }
}

現在看一下實現A的UIViewController子類：

class AController: UIViewController, A {
   override func viewDidLoad() {
      super.viewDidLoad()
      self.registerForNotification()
      triggerKeyboard()
   }

   func triggerKeyboard() {
      // Some code that make key board appear
   }

   func doA() {
   }
}

但令人驚訝的是，這會因錯誤而崩潰：

keyboardDidShow：]：無法識別的選擇器發送到實例0x7fc97adc3c60

那么我應該在視圖控制器本身中實現觀察者嗎？ 不能留在延期？

以下事情已經嘗試過。

制作A類協議。 將keyboardDidShow添加到協議本身作為簽名。

protocol A:class {
   func doA()
   func keyboardDidShow(notification: NSNotification)
}

Answer 1

我通過實現更新的- addObserverForName:object:queue:usingBlock: NSNotificationCenter的方法並直接調用方法解決了類似的問題。

extension A where Self: UIViewController  {
    func registerForNotification() {
        NSNotificationCenter.defaultCenter().addObserverForName(UIKeyboardDidShowNotification, object: nil, queue: nil) { [unowned self] notification in
            self.keyboardDidShow(notification)
        }
    }

    func keyboardDidShow(notification: NSNotification) {
        print("This will get called in protocol extension.")
    }
}

此示例將導致在協議擴展中調用keyboardDidShow 。

Answer 2

除了James Paolantonio的回答。 可以使用關聯對象實現unregisterForNotification方法。

var pointer: UInt8 = 0

extension NSObject {
    var userInfo: [String: Any] {
        get {
            if let userInfo = objc_getAssociatedObject(self, &pointer) as? [String: Any] {
                return userInfo
            }
            self.userInfo = [String: Any]()
            return self.userInfo
        }
        set(newValue) {
            objc_setAssociatedObject(self, &pointer, newValue, .OBJC_ASSOCIATION_RETAIN)
        }
    }
}

protocol A {}
extension A where Self: UIViewController {

    var defaults: NotificationCenter {
        get {
            return NotificationCenter.default
        }
    }

    func keyboardDidShow(notification: Notification) {
        // Keyboard did show
    }

    func registerForNotification() {
        userInfo["didShowObserver"] = defaults.addObserver(forName: .UIKeyboardDidShow, object: nil, queue: nil, using: keyboardDidShow)
    }

    func unregisterForNotification() {
        if let didShowObserver = userInfo["didShowObserver"] as? NSObjectProtocol {
            defaults.removeObserver(didShowObserver, name: .UIKeyboardDidShow, object: nil)
        }
    }
}

Answer 3

要避免崩潰，請在使用該協議的Swift類中實現observer方法。

實現必須在Swift類本身，而不僅僅是協議擴展，因為選擇器總是引用Objective-C方法，並且協議擴展中的函數不能用作Objective-C選擇器。 如果Swift類繼承自Objective-C類，則可以使用Swift類中的方法作為Objective-C選擇器

“如果您的Swift類繼承自Objective-C類，則該類中的所有方法和屬性都可用作Objective-C選擇器。”

此外，在Xcode 7.1， self必須垂頭喪氣到AnyObject指定其作為觀察者時addObserver調用。

protocol A {
    func doA()
}

extension A {
    func registerForNotification() {
        NSNotificationCenter.defaultCenter().addObserver(self as! AnyObject,
            selector: Selector("keyboardDidShow:"),
            name: UIKeyboardDidShowNotification,
            object: nil)
    }

    func keyboardDidShow(notification: NSNotification) {
        print("will not appear")
    }
}

class ViewController: UIViewController, A {
    override func viewDidLoad() {
        super.viewDidLoad()
        self.registerForNotification()
        triggerKeyboard()
    }

    func triggerKeyboard(){
        // Some code that makes the keyboard appear
    }

    func doA(){
    }

    func keyboardDidShow(notification: NSNotification) {
        print("got the notification in the class")
    }
}

Answer 4

在Swift中使用選擇器要求您的具體類必須從NSObject繼承。 要在協議擴展中強制執行此操作，您應該使用where 。 例如：

protocol A {
    func doA()
}

extension A where Self: NSObject {
  func registerForNotification() {
      NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("keyboardDidShow:"), name: UIKeyboardDidShowNotification, object: nil)
  }

  func keyboardDidShow(notification: NSNotification) {

  }
}

Answer 5

我使用NSObjectProtocol解決了它，如下所示，

@objc protocol KeyboardNotificaitonDelegate: NSObjectProtocol {
func keyboardWillBeShown(notification: NSNotification)
func keyboardWillBeHidden(notification: NSNotification)
}

extension KeyboardNotificaitonDelegate {

func registerForKeyboardNotifications() {
    //Adding notifies on keyboard appearing
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillBeShown(notification:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillBeHidden(notification:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
}

func deregisterFromKeyboardNotifications() {
    //Removing notifies on keyboard appearing
    NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardWillShow, object: nil)
    NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIKeyboardWillHide, object: nil)
}
}