Swift dispatch_async from function - ios

Question

How can i wait until function get all data from alamofire get request?
GetData.swift file:
import Foundation
import Alamofire
import SwiftyJSON
import ObjectMapper
func getStartData() -> Void {
let sharedBranch = BranchSingleton.sharedInstance
let sharedArticle = ArticleSingleton.sharedInstance
Alamofire.request(.GET, Config().apiBranch)
.responseJSON { request, response, result in
let jsonObj = SwiftyJSON.JSON(result.value!)
for obj in jsonObj {
let branch = Mapper<Branch>().map(obj.1.rawString()!)
sharedBranch.addBranch(branch!)
}
}
Alamofire.request(.GET, Config().apiArticle)
.responseJSON { request, response, result in
let jsonObj = SwiftyJSON.JSON(result.value!)
for obj in jsonObj {
let article = Mapper<Article>().map(obj.1.rawString()!)
sharedArticle.addArticle(article!)
}
}
}
ViewController.swift file:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
getStartData() // need to wait until all requests are finished then do print
print(sharedArticle.articleList)
}
}
SingletonObj.swift file:
import Foundation
class BranchSingleton {
var branchList: [Branch] = []
class var sharedInstance: BranchSingleton {
struct Static {
static let instance: BranchSingleton = BranchSingleton()
}
return Static.instance
}
func addBranch(branch: Branch) {
branchList.append(branch)
}
}
class ArticleSingleton {
var articleList: [Article] = []
class var sharedInstance: ArticleSingleton {
struct Static {
static let instance: ArticleSingleton = ArticleSingleton()
}
return Static.instance
}
func addArticle(article: Article) {
articleList.append(article)
}
}
i need to wait until getStartData() finish, then pring singleton array..
How can i do that?
This getStartData contains more than 2 requests, but i just gave example with 2..

Answer 1

You're asking a non-question. There is no reason to "wait". Nor can you. You just do what you do, asynchronously. Meanwhile the interface must stay active; the user must be able to continue to work. Thus there is nothing to "wait" for.
Now, if the question is, how can you send a signal in some elegant way to the rest of your app when all of the requests are done, one good answer is to use NSProgress. All the different requests can contribute to a common NSProgress object. The nice thing is that its fractionCompleted is observable with KVO, so when it comes greater-than-or-equal-to 1.0, you're done.
But you don't actually need the NSProgress; you could just increment or decrement an instance variable that's KVO-observable (being careful about threading, of course). If you know there are n processes, then you could just start a variable at n and have each process decrement it when it completes; a didSet observer on the variable can then take action when we hit zero.
The point is: you don't "wait": you just have all the different activities contribute to some common central value that "knows" when this means we've "finished" and can then take action.

Answer 2

As #Matt says, you can't, and shouldn't, try to wait until Alamofire is done with your request. That's like hiring somebody to run an errand for so you can work and then stopping everything and sitting by the door until they get back. You might as well have run the errand yourself.
Dropping the analogy, you might as well have performed the task synchronously. However, synchronous networking is a very bad idea. It freezes the UI until the network request is complete, which can be a very long wait if something goes wrong.
An async method like Alamofire's request method takes a completion block, a block of code that should be run when the work is finished.
The request method returns immediately, before the request has even been sent to the server, much less completed.
Instead of waiting around for the request to complete, you should refactor your getStartData method to take a completion handler, and use that to respond once the work is done:
func getStartData(completion: () -> void) -> Void {
let sharedBranch = BranchSingleton.sharedInstance
let sharedArticle = ArticleSingleton.sharedInstance
Alamofire.request(.GET, Config().apiBranch)
.responseJSON { request, response, result in
let jsonObj = SwiftyJSON.JSON(result.value!)
for obj in jsonObj {
let branch = Mapper<Branch>().map(obj.1.rawString()!)
sharedBranch.addBranch(branch!)
}
}
Alamofire.request(.GET, Config().apiArticle)
.responseJSON { request, response, result in
let jsonObj = SwiftyJSON.JSON(result.value!)
for obj in jsonObj {
let article = Mapper<Article>().map(obj.1.rawString()!)
sharedArticle.addArticle(article!)
}
//At this point the Alamofire .GET request for Config().apiArticle
//is complete. Call our completion block (passed in as a parameter)
completion()
}
}
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
getStartData()
{
//This is a "trailing closure", a block of code passed to getStartData
print("At this point, we've finished getting our data from Alamofire.")
print(sharedArticle.articleList)
}
}
}
Note that your getStartData method makes 2 Alamofire.request() commands in a row. If the second request requires that the first request be finished then you will need to restructure that code so that the second Alamofire request is inside the completion block for the first call. (That's more editing than I'm in the mood to do at the moment.)