How to check Alamofire request has completed - ios

Question

I am developing an iPad application using Swift. For http requests I use Alamofire library. So far I have managed to pull some data from an API. But the problem is since it is an asynchronous call I don't know how to check whether the request has completed. Any help would be appreciated.
This is the code I have implemented so far
Client class
func getUsers(completionHandler: ([User]?, NSError?) -> ()) -> (){
var users: [User] = []
let parameters = [
"ID": "123",
"apikey": "1234",
]
Alamofire.request(.GET, "API_URL", parameters: parameters).responseJSON() {
(_, _, JSON, error) in
let items = (JSON!.valueForKey("Users") as! [NSDictionary])
for item in items {
var user: User = User()
user.userId = item.valueForKey("ID")! as? String
user.userName = item.valueForKey("Name")! as? String
user.group = item.valueForKey("Group")! as? String
users.append(user)
}
completionHandler(users, error)
}
}
Main class
func getUsers(){
FacilityClient().getUsers() { (users, error) -> Void in
if users != nil {
self.users = users!
} else{
println("error - \(error)")
}
}
tableUsers.reloadData()
}
Thank you.

Answer 1

The closure part of the Alamofire request is called, when the request has completed. I've used your code and commented the line where the request hast finished:
Alamofire.request(.GET, "API_URL", parameters: parameters).responseJSON() {
(_, _, JSON, error) in
//
// The request has finished here. Check if error != nil before doing anything else here.
//
let items = (JSON!.valueForKey("Users") as! [NSDictionary])
for item in items {
var user: User = User()
user.userId = item.valueForKey("ID")! as? String
user.userName = item.valueForKey("Name")! as? String
user.group = item.valueForKey("Group")! as? String
users.append(user)
}
//
// After creating the user array we will call the completionHandler, which probably reports back to a ViewController instance
//
completionHandler(users, error)
}

Answer 2

If you want the tableView to reload data after successfully fetching data over network, you will need to call tableUsers.reloadData() inside that completion handler, like this:
func getUsers(){
FacilityClient().getUsers() { (users, error) -> Void in
if users != nil {
self.users = users!
tableUsers.reloadData() // SHOULD be here
} else{
println("error - \(error)")
}
}
// tableUsers.reloadData() // WAS here
}
And Alamofire make sure the completion handler is called on main queue if you don't specify a queue. You don't need to add code to make it be called on mainThread again.
And to your originally question: The only way Alamofire let you know a request has completed is by calling that completion handler which you give to the Alamofire.request method.