Swift使协议扩展成为通知观察者

问题描述

让我们考虑以下代码：

protocol A {
    func doA()
}

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

  func keyboardDidShow(notification: NSNotification) {

  }
}

现在看一下实现A的UIViewController子类：

Now look at a UIViewController subclass that implements A:

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

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

   func doA() {
   }
}

但令人惊讶的是，这会因错误而崩溃：

But surprisingly this crashes with an error:

ke yboardDidShow：]：无法识别的选择器发送到实例
0x7fc97adc3c60

那么我应该在视图控制器本身中实现观察者吗？不能留在延期？

So should I implement the observer in the view controller itself? Can't it stay in the extension?

已经尝试过的事情。

制作一个类协议。
将keyboardDidShow添加到协议本身作为签名。

making A a class protocol.Adding keyboardDidShow to protocol itself as signature.

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

推荐答案

我通过实现更新的 - addObserverForName：object：queue：usingBlock： NSNotificationCenter的方法并直接调用该方法。

I solved a similar problem by implementing the newer - addObserverForName:object:queue:usingBlock: method of NSNotificationCenter and calling the method directly.

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.")
    }
}

这个例子将是l导致在协议扩展中调用 keyboardDidShow 。

This example will cause keyboardDidShow to be called in the protocol extension.

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