Swift: Asynchronous callback

Question

How do I make asynchronous callbacks in swift? I'm writing a little Framework for my app because it's supposed to run on both, iOS und OS X. So I put the main code that is not device-specific into this framework that also handles requests to my online api. And obviously I also want the app's GUI and therefore my ViewControllers to react as soon as a api request has finished. In Objective-C I've done this by saving the view containing the function that had to be called in an id variable and the function itself in a selector variable. Then I invoked the function using the following code:

SEL selector = callbackMethod; ((void (*)(id, SEL))[callbackViewController methodForSelector:selector])(callbackViewController, selector); 

How can I accomplish this in swift? Or is there a better way of doing this?

I really appreciate all your help!

Answer 1

I've shared the pattern that I use for this scenario in the following gist: https://gist.github.com/szehnder/84b0bd6f45a7f3f99306

Basically, I create a singleton DataProvider.swift that setups an AFNetworking client. Then the View Controllers call methods on that DataProvider, each of which is terminated by a closure that I've defined as a typealias called ServiceResponse. This closure returns either a dictionary or an error.

It allows you to very cleanly (imo) call for an async data action from the VC's with a very clear indication of what you want performed when that async response returns.

DataProvider.swift

typealias ServiceResponse = (NSDictionary?, NSError?) -> Void  class DataProvider: NSObject {      var client:AFHTTPRequestOperationManager?     let LOGIN_URL = "/api/v1/login"      class var sharedInstance:DataProvider {         struct Singleton {             static let instance = DataProvider()         }         return Singleton.instance     }      func setupClientWithBaseURLString(urlString:String) {         client = AFHTTPRequestOperationManager(baseURL: NSURL.URLWithString(urlString))         client!.operationQueue = NSOperationQueue.mainQueue()         client!.responseSerializer = AFJSONResponseSerializer()         client!.requestSerializer = AFJSONRequestSerializer()     }      func loginWithEmailPassword(email:String, password:String, onCompletion: ServiceResponse) -> Void {         self.client!.POST(LOGIN_URL, parameters: ["email":email, "password":password] , success: {(operation:AFHTTPRequestOperation!, responseObject:AnyObject!) -> Void in              self.setupClientWithBaseURLString("http://somebaseurl.com")              let responseDict = responseObject as NSDictionary                 // Note: This is where you would serialize the nsdictionary in the responseObject into one of your own model classes (or core data classes)                 onCompletion(responseDict, nil)             }, failure: {(operation: AFHTTPRequestOperation!, error:NSError!) -> Void  in                 onCompletion(nil, error)             })     } } 

MyViewController.swift

import UIKit  class MyViewController: UIViewController {      override func viewDidLoad() {         super.viewDidLoad()          // Do any additional setup after loading the view.     }      override func viewWillAppear(animated: Bool)  {         super.viewWillAppear(animated)         DataProvider.sharedInstance.loginWithEmailPassword(email:"[email protected]", password:"somepassword") { (responseObject:NSDictionary?, error:NSError?) in              if (error) {                 println("Error logging you in!")             } else {                 println("Do something in the view controller in response to successful login!")             }         }     }   }