Notification center

class functionPair {
    let target : NSObject
    let selector : Selector
    init(_ selet : Selector, _ target : NSObject) {
        self.target = target
        self.selector = selet
    }
}


class NotificationCenter {
    static let shared = NotificationCenter()
    var map :[String: [functionPair]]

    private init(){
        map = [String: [functionPair]]()
    }

    func addObserver(_ event: String, _ selector : Selector, _ target: NSObject){
        let pair = functionPair(selector, target)
        map[event, default : [functionPair]()].append(pair)
    }

    func postEvent(_ event: String){
        if let list = map[event]{
            for pair in list {
                pair.target.perform(pair.selector)
            }
        }
    }
    func removeObserver(_ event: String, _ target: NSObject) {
        if let list = map[event]{
            map[event] = list.filter{  $0.target !== target}
        }
    }

}
class obj2 : NSObject{
    @objc func printSelf(){
        print("im obj2")
    }
}

class obj1 : NSObject{
    @objc func printSelf(){
        print("im obj1")
    }

    @objc func printNumber(){
        print("number number")
    }
}

let o1 = obj1()
let o2 = obj2()

NotificationCenter.shared.addObserver("event1", #selector(o1.printSelf), o1)
NotificationCenter.shared.addObserver("event1", #selector(o2.printSelf), o2)
NotificationCenter.shared.addObserver("event2", #selector(o1.printNumber), o1)



NotificationCenter.shared.postEvent("event1")
NotificationCenter.shared.postEvent("event2")
NotificationCenter.shared.removeObserver("event1", o1)
NotificationCenter.shared.postEvent("event1")