Return value from swift function with background code - xcode

Question

The function below is only returning false, probably because the user.singUpInBackgroundWithBlock is happening in background.
Is there anyway that I can get the intended return value from the function?
var returnFlag:Bool = false
func signUpAction(email:String, password:String) -> Bool
{
let user = PFUser()
user.username = email
user.password = password
user.signUpInBackgroundWithBlock {
(succeeded: Bool, error: NSError?) -> Void in
if let error = error {
let errorString = error.userInfo["error"] as? NSString
print(errorString!)
// INTENDED RETURN
self.returnFlag = false
} else {
// INTENDED RETURN
self.returnFlag = true
}
}
return self.returnFlag
}

Answer 1

You are right, the function will return false because the block is probably not called on the main thread.
This is an ideal scenario to use NSNotification. Do not pass a return value, instead post a notification once the login action is complete.
Sample Code :
Somewhere early in your view controller lifecycle, preferably viewdidload. Register your class to observer for login success and login failed notifications.
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("LoginFailedFunc:"), name: "loginFailed", object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("loginSuccessFunc:"), name: "loginSuccess", object: nil)
In your login function, post a notification based on valid or invalid login.
func signUpAction(email:String, password:String){
let user = PFUser()
user.username = email
user.password = password
user.signUpInBackgroundWithBlock {
(succeeded: Bool, error: NSError?) -> Void in
if let error = error {
let errorString = error.userInfo["error"] as? NSString
print(errorString!)
// INTENDED RETURN
NSNotificationCenter.defaultCenter().postNotificationName("loginFailed", object: self)
self.returnFlag = false
} else {
NSNotificationCenter.defaultCenter().postNotificationName("loginSuccess", object: self)
self.returnFlag = true
}
}
}
Finally remember to stop observing notificaitons, when no longer required.