How to set an identifier for 'error' in alamofire for login page

Question

I am trying to set an error identifier so a user gets an error message in a errorLabel if the info they typed in is wrong. I tried to put 'error' in { (response) in but that threw errors. What is a good way to handle this.

AF.request(url, method: .post, parameters: parameters as Parameters, encoding: URLEncoding.default).response { (response) in

            print(response)

           if  error != nil {
               // Couldn't sign in
               self.errorLabel.text = error!.localizedDescription
               self.errorLabel.alpha = 1
           }
           else {

               let tabBarController =
                   self.storyboard?.instantiateViewController(identifier: Constants.Storyboard.TabBarController) as? UITabBarController

               self.view.window?.rootViewController = tabBarController
               self.view.window?.makeKeyAndVisible()
            }
          }
        }

Answer 1

You can identify error using switch case in alamofire.

AF.request(url, method: .post, parameters: parameters as Parameters, encoding: 
URLEncoding.default).response { (response) in

        switch response.result {
             case .success:
             //sign in
             let tabBarController =
             self.storyboard?.instantiateViewController(identifier: Constants.Storyboard.TabBarController) as? UITabBarController
             self.view.window?.rootViewController = tabBarController
             self.view.window?.makeKeyAndVisible()

             case .failure(let error):
             // Couldn't sign in
             self.errorLabel.text = error!.localizedDescription
             self.errorLabel.alpha = 1
        }
      }