--- title: User Log In slug: docs/ios/parse-swift-sdk/users/user-log-in description: In this guide you'll learn how to log in and log out a user in iOS using the ParseSwift SDK image: https://www.back4app.com/images/logo-social.png docTags: createdAt: 2024-03-11T15:50:36.344Z --- # User log in and log out ## Introduction In the [user registration guide](https://www.back4app.com/docs/ios/parse-swift-sdk/users/user-registration) we learned how to integrate a signup option into an iOS app using the **Back4App** platform and the `ParseSwift SDK`. Once a user successfully signs up in your app, logging in and logging out actions are key features within the app’s flow. The `ParseSwift SDK` will allow us to integrate these features seamlessly into any iOS app. ## Prerequisites :::hint{type="info"} **To complete this quickstart, you need:** - Xcode. - An app created at Back4App. - Follow the [New Parse App tutorial](https://www.back4app.com/docs/get-started/new-parse-app) to learn how to create a Parse app at **Back4App**. - **Note: **Follow the [Install Parse SDK (Swift) Tutorial](https://www.back4app.com/docs/ios/parse-swift-sdk) to create an Xcode Project connected to **Back4App**. ::: ## Goal To implement a user login and logout feature using the **ParseSwift SDK** and the **Back4App** platform. ## 1 - Setting up the login and logout features Before starting to implement any login functionality, we have to create the object that will represent the user. For simplicity, we will reuse the same `User` struct (which conforms to the `ParseUser` protocol) we introduced in the [user registration guide](https://www.back4app.com/docs/ios/parse-swift-sdk/users/user-registration): ```swift import Foundation import ParseSwift struct User: ParseUser { ... var username: String? var email: String? var emailVerified: Bool? var password: String? var age: Int? } ``` We recommend following the user registration guide and registering at least one user to use it as an example for this guide. Similar to the signup process, logging in requires a form where the user enters their **username** and **password**. Then, we perform a login request using the corresponding methods provided by the `ParseSwift SDK`. In its turn, **Back4App** processes the request and returns a response containing the login information. When an error occurs, the response returns information to identify and handle this error. The logout process is straightforward. The `ParseSwift SDK` allows us to implement it in a single line of code. ## 2 - Setting up the app Once you [connected](https://www.back4app.com/docs/ios/parse-swift-sdk/install-sdk) your Xcode project to your **Back4App** application, the next step is to set up the app’s user interface. For the login process, we will implement a simple controller containing the corresponding input fields and a login button: ::Image[]{src="https://api.archbee.com/api/optimize/yD3zCY-NNBBIfd0uqcfR5/C2xjVDNgWjfrg49Nlicjz_image.png" size="40" width="1170" height="2532" position="center" showCaption="false"} The class in charge of this form is called LogInController and it is a subclass of UIViewController. The key components to integrate into this controller are two UITextField’s and one UIButton. The following snippet shows the implementation of the LogInController class: ```swift 1 import UIKit 2 import ParseSwift 3 4 class LogInController: UIViewController { 5 private let usernameTextField: UITextField = { 6 let textField = UITextField() 7 textField.borderStyle = .roundedRect 8 textField.placeholder = "Username *" 9 textField.autocapitalizationType = .none 10 textField.textAlignment = .center 11 return textField 12 }() 13 14 private let passwordTextField: UITextField = { 15 let textField = UITextField() 16 textField.borderStyle = .roundedRect 17 textField.isSecureTextEntry = true 18 textField.placeholder = "Password *" 19 textField.textAlignment = .center 20 return textField 21 }() 22 23 private let logInButton: UIButton = { 24 let button = UIButton(type: .roundedRect) 25 button.setTitle("Log in", for: .normal) 26 return button 27 }() 28 29 override func viewDidLoad() { 30 super.viewDidLoad() 31 32 navigationItem.title = "Back4App Log In" 33 34 // Lays out the login form 35 let stackView = UIStackView(arrangedSubviews: [usernameTextField, passwordTextField, logInButton]) 36 stackView.translatesAutoresizingMaskIntoConstraints = false 37 stackView.spacing = 8 38 stackView.axis = .vertical 39 stackView.distribution = .fillEqually 40 41 let stackViewHeight = CGFloat(stackView.arrangedSubviews.count) * (44 + stackView.spacing) - stackView.spacing 42 43 view.addSubview(stackView) 44 stackView.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor).isActive = true 45 stackView.centerYAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerYAnchor).isActive = true 46 stackView.widthAnchor.constraint(equalTo: view.safeAreaLayoutGuide.widthAnchor, multiplier: 0.7).isActive = true 47 stackView.heightAnchor.constraint(equalToConstant: stackViewHeight).isActive = true 48 49 // Adds the method that will be called when the user taps the login button 50 logInButton.addTarget(self, action: #selector(handleLogIn), for: .touchUpInside) 51 52 // If the user is already logged in, we redirect them to the HomeController 53 guard let user = User.current else { return } 54 let homeController = HomeController() 55 homeController.user = user 56 57 navigationController?.pushViewController(homeController, animated: true) 58 } 59 60 /// Called when the user taps on the logInButton button 61 @objc private func handleLogIn() { 62 guard let username = usernameTextField.text, !username.isEmpty, 63 let password = passwordTextField.text, !password.isEmpty else { 64 // Shows an alert with the appropriate title and message. 65 return showMessage(title: "Error", message: "Invalid credentials.") 66 } 67 68 logIn(with: username, password: password) 69 } 70 71 /// Logs in the user and presents the app's home screen (HomeController) 72 /// - Parameters: 73 /// - username: User's username 74 /// - password: User's password 75 private func logIn(with username: String, password: String) { 76 // TODO: Here we will implement the login process 77 } 78 } ``` Additionally, the helper function `showMessage(title:message:)` is implemented in an extension of `UIViewController`: ```swift 1 extension UIViewController { 2 3 /// Presents an alert with a title, a message and a back button. 4 /// - Parameters: 5 /// - title: Title for the alert 6 /// - message: Shor message for the alert 7 func showMessage(title: String, message: String) { 8 let alertController = UIAlertController(title: title, message: message, preferredStyle: .alert) 9 10 alertController.addAction(UIAlertAction(title: "Back", style: .cancel)) 11 12 present(alertController, animated: true) 13 } 14 } ``` For the logout process, we insert a button in the home controller, i.e., `HomeController`. This view controller will only contain the logout button and a label showing the user’s username: ::Image[]{src="https://api.archbee.com/api/optimize/yD3zCY-NNBBIfd0uqcfR5/M3zOsTaYq0bCTkdE2zDRK_image.png" size="40" width="1170" height="2532" position="center" showCaption="false"} The implementation of this view controller is straightforward: ```swift 1 import UIKit 2 import ParseSwift 3 4 class HomeController: UIViewController { 5 6 /// When set, it updates the usernameLabel's text with the user's username. 7 var user: User? { 8 didSet { 9 usernameLabel.text = "Hello \(user?.username ?? "N/A")!" 10 } 11 } 12 13 private let usernameLabel: UILabel = { 14 let label = UILabel() 15 label.textAlignment = .center 16 label.font = .boldSystemFont(ofSize: 18) 17 label.translatesAutoresizingMaskIntoConstraints = false 18 return label 19 }() 20 21 private let logOutButton: UIButton = { 22 let button = UIButton(type: .roundedRect) 23 button.setTitle("Log out", for: .normal) 24 button.translatesAutoresizingMaskIntoConstraints = false 25 return button 26 }() 27 28 override func viewDidLoad() { 29 super.viewDidLoad() 30 31 // Sets up the layout (usernameLabel and logOutButton) 32 view.backgroundColor = .systemBackground 33 navigationItem.hidesBackButton = true 34 navigationItem.title = "Back4App" 35 view.addSubview(usernameLabel) 36 view.addSubview(logOutButton) 37 38 usernameLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 8).isActive = true 39 usernameLabel.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor).isActive = true 40 41 logOutButton.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor, constant: 8).isActive = true 42 logOutButton.centerXAnchor.constraint(equalTo: view.safeAreaLayoutGuide.centerXAnchor).isActive = true 43 44 // Adds the method that will be called when the user taps the logout button 45 logOutButton.addTarget(self, action: #selector(handleLogOut), for: .touchUpInside) 46 } 47 48 /// Called when the user taps the logout button. 49 @objc private func handleLogOut() { 50 // TODO: Here we will implement the logout process 51 } 52 } ``` ## 3 - Login request We now proceed to implement the **logIn(with\:password)** method in the **LogInController** class. The **ParseUser** protocol gives the **User** object the static method **login(username\:password)**. This method prepares and sends the login request to your **Back4App** application. Depending on the use case, one can use one of the many implementations of the **login(...)** method. We now complete the **logIn(with\:password)** method in **LogInController**: ```swift 1 class HomeController: UIViewController { 2 ... 3 4 /// Logs in the user and presents the app's home screen (HomeController) 5 /// - Parameters: 6 /// - username: User's username 7 /// - password: User's password 8 private func logIn(with username: String, password: String) { 9 // WARNING: Use only one of the following implementations, the synchronous or asynchronous option 10 11 // Logs in the user synchronously, it throws a ParseError error if something happened. 12 // This should be executed in a background thread! 13 do { 14 let loggedInUser = try User.login(username: username, password: password) 15 16 // After the login success we send the user to the home screen 17 let homeController = HomeController() 18 homeController.user = loggedInUser 19 20 navigationController?.pushViewController(homeController, animated: true) 21 } catch let error as ParseError { 22 showMessage(title: "Error", message: "Failed to log in: \(error.message)") 23 } catch { 24 showMessage(title: "Error", message: "Failed to log in: \(error.localizedDescription)") 25 } 26 27 // Logs in the user asynchronously 28 User.login(username: username, password: password) { [weak self] result in // Handle the result (of type Result) 29 switch result { 30 case .success(let loggedInUser): 31 self?.usernameTextField.text = nil 32 self?.passwordTextField.text = nil 33 34 // After the login success we send the user to the home screen 35 let homeController = HomeController() 36 homeController.user = loggedInUser 37 38 self?.navigationController?.pushViewController(homeController, animated: true) 39 case .failure(let error): 40 self?.showMessage(title: "Error", message: "Failed to log in: \(error.message)") 41 } 42 } 43 } 44 } ``` ## 4 - Logout request The logout request is as simple as the login request. Once again, the **ParseUser** protocol provides the **User** with the static method **logout(...)**. By calling this method the current user (accessed via **User.current**) logs out from your **Back4App** application. We will call this method when the user taps the logout button located on the home screen, i.e., in the **handleLogOut()** method in the **HomeController** class, we add the following: ```swift 1 class HomeController: UIViewController { 2 ... 3 4 /// Called when the user taps the logout button. 5 @objc private func handleLogOut() { 6 // WARNING: Use only one of the following implementations, the synchronous or asynchronous option 7 8 // Logs out the user synchronously, it throws a ParseError error if something happened. 9 // This should be executed in a background thread! 10 do { 11 try User.logout() 12 13 // After the logout succeeded we dismiss the home screen 14 navigationController?.popViewController(animated: true) 15 } catch let error as ParseError { 16 showMessage(title: "Error", message: "Failed to log out: \(error.message)") 17 } catch { 18 showMessage(title: "Error", message: "Failed to log out: \(error.localizedDescription)") 19 } 20 21 // Logs out the user asynchronously 22 User.logout { [weak self] result in // Handle the result (of type Result) 23 switch result { 24 case .success: 25 // After the logout succeeded we dismiss the home screen 26 self?.navigationController?.popViewController(animated: true) 27 case .failure(let error): 28 self?.showMessage(title: "Error", message: "Failed to log out: \(error.message)") 29 } 30 } 31 } 32 } ``` ## 5 - Run the app! In this [repository](https://github.com/templates-back4app/ios-user-log-in-and-log-out), you will find an Xcode project containing the login and logout processes we described above. Before running the app, make sure you connected the Xcode project to your `Back4App` application. ## Conclusion The **Back4App** and the `ParseSwift SDK` allow us to integrate login and logout features in iOS apps in a quick way. After connecting your **Back4App** application with your Xcode project, the login (or logout) process only requires calling a single method.