ACM_Someone like you

  @Published var foo:String = "test" //@Published是Combine的修飾屬性，標識這是個被觀察的對象 即發布者 

  let subscription = $foo.sink { print("foo is \($0)") }//發布者通過 sink 訂閱 Publisher 事件
  
  foo = "\(indexPath.row)" //發布者對象發生變化時候 Subscriber 監聽到就會執行 sink

//?? 如果發現只執行了一次監聽 或者 無法監聽 是因為Subscriber 訂閱者訂閱的數據流的作用域問題，可考慮把發布者或者訂閱者設計為實例變量持有即可

PassthroughSubject 發布者：狀態管理外部數據監聽
//創建一個實際的傳遞主題實例 默認初始化器
 let passThroughSubject = PassthroughSubject<String, Error>()
//先訂閱
        let subscription = passThroughSubject.sink(
                    receiveCompletion: { completion in
                        print("Received completion (sink)", completion)
                },
                    receiveValue: { value in
                        print("Received value (sink)", value)
                    }).store(in: &cancellables)
//??如果沒有store 方法 只執行一次，需要把訂閱者存住The set in which to store this ``AnyCancellable``.
//后接收            
passThroughSubject.send("Hello1 ")
passThroughSubject.send("Hello2”)

let downloadPublisher =  Future<Data?, Error> { promise in
            URLSession.shared.dataTask(with: URL.init(string: "https:www.1")!) { ( data, response, error) in
                if (data != nil) && error == nil {
                    promise(.success(data))
                } else {
                    promise(.failure(error!))
                }
            }.resume()
        }
        
        let cancellable = downloadPublisher.sink { (result) in
            switch result {
            case .failure(let error):
                Log(error.localizedDescription)
            default: break
            }
        } receiveValue: {  value in
            print("Received value (sink)", value)
        }.store(in: &cancellables)

//需要取消監聽

cancellable.cancel()