把下边的code放在storyboard中执行（灵活的注释一些行），可以看到一下效果：
1.多次addObserver，会导致对应的方法执行多次；
2.多次addObserver，一次remove，虽然不能把多有notification移除掉，但是只要所在容器类析构，就会移除掉其所有的notification
import UIKit
let customNotification: String = "customNotification"
class Manager {
deinit {
print("deinit")
NSNotificationCenter.defaultCenter().removeObserver(self, name: customNotification, object: nil)
}
init() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(Manager.notificationHandler(_:)), name: customNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(Manager.notificationHandler(_:)), name: customNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(Manager.notificationHandler(_:)), name: customNotification, object: nil)
}
func postNotification() {
NSNotificationCenter.defaultCenter().postNotificationName(customNotification, object: nil, userInfo: nil)
}
@objc func notificationHandler(notification: NSNotification) {
print("notificationHandler")
}
}
var manager: Manager? = Manager()
manager?.postNotification()
manager = nil
NSNotificationCenter.defaultCenter().postNotificationName(customNotification, object: nil, userInfo: nil)
