How can I trigger async requests out of view controller - swift

Question

I am building an iOS app and I just finished my login/register part ( requesting a sails.js rest Api)
At the moment I have 2 view controllers with duplicate code because i issue the rest calls on register/login button event listener of each class and there is a lot of similar code I can refactor.
What I want to do is to create a singleton called ApiManager that will contain all the calls that I need. (And the futur ones )
The problem is that with async calls I can't create a function func login(username,password) that will return data so I can store them and prepareforsegue.
What is the simple/proper way to achieve that correctly? Which means call ApiManager.myFunction and using the result wherever it's needed ( filling a tableview for data, initiating a segue for login or register with succes ) and to make this function reusable in another view controller even if it is for another usage. I am using swift.
EDIT : Here is how i did it so i hope it will help you
The function executing the rest call :
func login(#username: String, password: String, resultCallback: (finalresult: UserModel!,finalerror:String!) -> Void) {
Alamofire.request(.POST, AppConfiguration.ApiConfiguration.apiDomain+"/login", parameters: ["username": username,"password": password], encoding: .JSON)
.responseJSON { request, response, data, error in
if let anError = error
{
resultCallback(finalresult: nil,finalerror:anError.localizedDescription)
}else if(response!.statusCode == 200){
var user:UserModel = self.unserializeAuth(data!)//just processing the json using SwiftyJSON to get a easy to use object.
resultCallback(finalresult: user,finalerror:nil)
}else{
resultCallback(finalresult: nil,finalerror:"Username/Password incorrect!")
}
}.responseString{ (request, response, stringResponse, error) in
// print response as string for debugging, testing, etc.
println(stringResponse)
}
}
And this is how i call this function from my ViewController :
#IBAction func onLoginTapped(sender: AnyObject) {//When my user tap the login button
let username = loginInput.text;//taking the content of inputs
let password = passwordInput.text;
ApiManager.sharedInstance.login(username:username,password:password){
[unowned self] finalresult,finalerror in
if(finalresult !== nil){//if result is not null login is successful and we can now store the user in the singleton
ApiManager.sharedInstance.current_user=finalresult
self.performSegueWithIdentifier("showAfterLogin", sender: nil)//enter the actual app and leave the login process
}else{
self.displayAlert("Error!", message: finalerror)//it is basically launching a popup to the user telling him why it didnt work
}
}
}

Answer 1

Almost all of my apps end up with a Server class which is the only one that knows how to communicate with the server. It makes the call, parses the result into a Swift struct and returns it. Most of my servers return json so I use SwiftyJSON, but you can do whatever you want.
The point is, that since this is the only class that knows about server communication, if I need to change the library being used to do the communication (AFNetworking 1 vs 2 vs Parse, vs whatever) this is the only class I need to touch.
class Server {
static let instance = Server()
func loginWithUsername(username: String, password: String, resultCallback: (result: Either<User, NSError>) -> Void) {
// if login is successful call
resultCallback(result: .Left(self.user!))
// otherwise call
resultCallback(result: .Right(error))
}
}
An example of use:
let server = Server.instance
SVProgressHUD.showWithStatus("Loggin In...")
server.loginWithUsername(username, password: password) { [unowned self] result in
SVProgressHUD.dismiss()
switch result {
case .Left(let user):
self.presentUserType(user.userType)
case .Right(let error):
self.warnUserWithMessage("An error occured. \(error.localizedDescription)")
}
}
If the username/password are needed for all subsequent calls, then the server object will maintain a copy of them. If the login returns a token, then the server keeps a copy of that.
QED.

Answer 2

I usually have utility functions in a base class shared by my view controllers and use NSNotificationCenter for reacting to the results of the requests. It can also easily be achieved through delegation (protocol & delegate.
It is mostly about perception but I find it is easier to visualize that you can, for example, start an action on one controller and react on another because the call took this long and you were not blocking navigation in your app.