多次回调，而不是迅速使用代理

Question

I am developing an app that have to send commands to a machine. I know how to use delegates to propagate the response of the commands that I receive in an Input Stream. But probably is better to use Callbacks for some commands who have to update the UI.

I have searched for a good solution to code this, but I couldn't find it.

In this code, for example:

class NetworkService {

    var onComplete: ((result: String)->())? //an optional function

    func fetchDataFromUrl(url: String) {
        API.request(.GET, url) { result in
            onComplete?(result: result) 
    }
}

class MyViewController: UIViewController {

    let networkService = NetworkService()

    override func viewDidLoad() {
        super.viewDidLoad()
        networkService.onComplete = { result in
            print("I got \(result) from the server!")
        }
    }
}

It's ok, I can use onComplete as a callback, but... I need multiple callbacks for multiple commands:

• Have I to create a "var" with the callback for each different command?
• Is there a way to have an array or a queue with the callbacks?
• What will happen If I don't receive a response for a command, and I send again the command? I suppose that I have to handle timeouts in some way.
• What could be the best way to solve this problem?

Answer 1

Have you tried notifications? on your ViewDidLoad:

override func viewDidLoad() {
    super.viewDidLoad()

    NotificationCenter.default.addObserver(self, selector: #selector(dataFetched), name: NSNotification.Name(rawValue: "dataFetched"), object: nil)
    networkService.fetchDataFromUrl(url: url)
}

func dataFetched(_ notification: Notification) {
    // do your stuff with notification.object
}

on your NetworkService class

func fetchDataFromUrl(url: String) { 
    API.request(.GET, url)
}

func dataFetched(result: Any) {
    NotificationCenter.default.post(name: NSNotification.Name(rawValue: "dataFetched"), object: result)
}