Waiting for Callback Function to Finish : Swift - swift

Question

I want to change the view when the user logs in from the LoginController. When access = true, change controller. However, I cant do it within the user.login because it gives me an error saying I have to process this on the main thread. Now I know that there are solutions for this, but I have been searching for a week and ran around in circles. I have gotten close enough to produce what I have below.
I have 3 pieces of information that I would like to share:
LoginController:
var access = false
user.login(
{(response: Bool) -> () in
access = response
print(access)
},username: emailField.text!, password: passwordField.text!)
if(access){
print("YAY")
let controller = storyboard?.instantiateViewControllerWithIdentifier("NewsFeed") as! NewsFeed
presentViewController(controller, animated: true, completion: nil)
}else{
print("NAY")
}
LoginClass:
func login(completionHandler : (response: Bool) -> (), username: String, password: String){
//Set the calback with the calback in the function parameter
let parameters : [String: AnyObject] = ["tag": "login", "email": username, "password": password]
manager.postDataToServer(
{(response: NSDictionary) -> () in
if(response["success"] as! Int == 1){
// Log user in
}else{
// User not able to login
}
completionHandler(response: false)
}
}, page: "login", params: parameters)
}
APIManager:
func postDataToServer(completionHandler: (response: NSDictionary) -> (), page: String, params: [String: AnyObject]){
// Gets the information and returns the User
// Works completely fine
}
ANSWER : Please go down to look at the Updated Answer
Please look at #Rob's answer. However you may get an error message saying Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '-[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.'. It is because you cannot change views unless its on the main thread. Simply wrap it in
NSOperationQueue.mainQueue().addOperationWithBlock {
//Change View
}
Updated
I realized my mistake was that I didn't endEditing in one of my fields before processing the information. I fixed it by doing the following, passwordField.endEditing and also emailField.endEditing (just to be safe)

Answer 1

Instead of waiting for the response, just move the code you want to perform inside the closure:
user.login( { response in
if response {
print("YAY")
let controller = self.storyboard?.instantiateViewControllerWithIdentifier("NewsFeed") as! NewsFeed
self.presentViewController(controller, animated: true, completion: nil)
} else {
print("NAY")
}
}, username: emailField.text!, password: passwordField.text!)
Even better, I'd change the order of those parameters, so that the closure was the last parameter (and you can then use "trailing closure" syntax):
func loginWithUsername(username: String, password: String, completionHandler : (response: Bool) -> ()) {
// your login code here
}
And then:
user.loginWithUsername(emailField.text!, password: passwordField.text!) { response in
if response {
print("YAY")
let controller = self.storyboard?.instantiateViewControllerWithIdentifier("NewsFeed") as! NewsFeed
self.presentViewController(controller, animated: true, completion: nil)
} else {
print("NAY")
}
}