How can I wait for the result of the POST call in swift?

Question

I'm using the google api for ios for signing in to the mobile app (taken from here: https://developers.google.com/identity/sign-in/ios/backend-auth They are showing there how to use objective-c to make a post request to the backend server and as a result - get the info if the token is valid or not.

I established my backend server properly and it verifies if the token is good or not (and it returns the status 200 or 401. Now I just need to send the token from the app to my server and based on its result validate the user or not.

I found this answer about making post requests: https://stackoverflow.com/a/26365148/4662074

and following this example I coded it as follows:

// [START signin_handler]
func signIn(signIn: GIDSignIn!, didSignInForUser user: GIDGoogleUser!,
    withError error: NSError!) {
        if (error == nil) {
            print("!!!! TOKEN !!!! "+user.authentication.idToken)

            let request = NSMutableURLRequest(URL: NSURL(string: "http://mywebserver.com:3000/auth/token")!)
            request.HTTPMethod = "POST"
            let postString = "id_token="+user.authentication.idToken
            request.HTTPBody = postString.dataUsingEncoding(NSUTF8StringEncoding)
            let task = NSURLSession.sharedSession().dataTaskWithRequest(request) { data, response, error in
                guard error == nil && data != nil else {                                                          // check for fundamental networking error
                    print("error=\(error)")
                    return
                }

                if let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 {           // check for http errors
                    print("statusCode should be 200, but is \(httpStatus.statusCode)")
                    print("response = \(response)")
                }

                let responseString = NSString(data: data!, encoding: NSUTF8StringEncoding)
                print("responseString = \(responseString)")


                print("Signed in as a user: "+user.profile.name)

            }
            task.resume()

            let sb = UIStoryboard(name: "Main", bundle: nil)
            if let tabBarVC = sb.instantiateViewControllerWithIdentifier("TabController") as? TabController {
                self.window!.rootViewController = tabBarVC
            }

        } else {
            print("\(error.localizedDescription)")

        }
}
// [END signin_handler]

Ok, in this case right after making a call to the webservice I'm switching the view to the main page of the app:

let sb = UIStoryboard(name: "Main", bundle: nil)
                if let tabBarVC = sb.instantiateViewControllerWithIdentifier("TabController") as? TabController {
                    self.window!.rootViewController = tabBarVC
                }

But since I'm doing it right after task.resume() - that means I'm never waiting for the result from the webservice and even if it states 401 - user is still signed it. I tried to put that piece of code above the task.resume() but then I'm getting error:

This application is modifying the autolayout engine from a background thread, which can lead to engine corruption and weird crashes.  This will cause an exception in a future release.

So how can I include the answer from my webservice during the logging in process and if the status is 200 - then switch the view to my TabController? (and in other cases for example ask the user to log in again)

score 1 · Accepted Answer · answered Feb 13 '16 at 15:48

1

Tell, don't wait.

The request works asynchronously, so instantiate you controller in the completion block on success. To avoid the auto layout engine message you have to do that on the main thread.

       ...
       print("Signed in as a user: "+user.profile.name)

       dispatch_async(dispatch_get_main_queue()) {
          let sb = UIStoryboard(name: "Main", bundle: nil)
          if let tabBarVC = sb.instantiateViewControllerWithIdentifier("TabController") as? TabController {
            self.window!.rootViewController = tabBarVC
          }
       }
     }
     task.resume()
   } else { ... }

answered Feb 13 '16 at 15:48

vadian

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Ok, thank you, that makes sense, but I see I have to do it only if the status is 200 - can you tell me, based on my code, how can I check it? – randomuser1 Feb 13 '16 at 16:01
Just add a `return` statement when the response code is checked like in the `guard` expression. – vadian Feb 13 '16 at 16:04
sorry if that's a tedious question, I added `return` just after `print("response = \(response)")` but now when I want to include `httpStatus` in an if statement later on I'm getting `use of unresolved value httpStatus` - what am I doing wrong? – randomuser1 Feb 13 '16 at 16:14
1

use `guard let httpStatus = response as? NSHTTPURLResponse where httpStatus.statusCode != 200 else { print .. return } ` – vadian Feb 13 '16 at 16:16

How can I wait for the result of the POST call in swift?

1 Answers1