Android

Login and User registration tutorial

Introduction

In this section we will take a look to how to create an app with a simple user registration using Parse Server core features through Back4App.

This tutorial uses a basic app created in Android Studio 4.1.1 with buildToolsVersion=30.0.2 , Compile SDK Version = 30.0.2 and targetSdkVersion 30

At any time, you can access the complete Project via our GitHub repositories.

• Kotlin Example Repository
• Java Example Repository

Goal

We will learn how to log in and register using Parse.

Here is a preview of what we are gonna achive :

Prerequisites

For complete this tutorial, we need:

• Android Studio.
• An app created on Back4App.
  • Note: Follow the New Parse App tutorial to learn how to create a Parse App on Back4App.
• An android app connected to Back4app.
  • Note: Follow the Install Parse SDK tutorial to create an Android Studio Project connected to Back4App.
• A device (or virtual device) running Android 4.1 (Jelly Bean) or newer.

Step 1 - Import Library

In this step we will import the libraries which we are gonna use in our project:

1. We will add following Parse Classes to our Activities.

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    import com.parse.Parse;
    import com.parse.ParseException;
    import com.parse.ParseUser;
   

2. We will use lambda functions frequently in our project because of that we need to add Java 1.8 to our project via build.gradle(Module:App)

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    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
   

Step 2 - Sign Up

Signing up basically creates a new Parse.User Object in User Class, shown as “User” in your app Dashboard. We need to set at least two properties when creating a new user => ParseUser.setUsername() and ParseUser.setPassword().

The method used for saving the new user on Android is ParseUser.signUpInBackground(), which may come together with a callback function.

Note: Objects of this special class are not saved on the Dashboard with ParseObject.save() method.

To make SignUpActivity work, follow these steps:

1. Import

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   import com.parse.SignUpCallback;
   

   into your SignUpActivity, in addition to the dependencies imported in Step 1.

2. To implement user registration, simply use the following code in the onCreate() method:

   • Java
   • Kotlin

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   ParseUser user = new ParseUser();
        // Set the user's username and password, which can be obtained by a forms
        user.setUsername( "<Your username here>");
        user.setPassword( "<Your password here>");
        user.signUpInBackground(new SignUpCallback() {
            @Override
            public void done(ParseException e) {
                if (e == null) {
                    showAlert("Successful Sign Up!", "Welcome" + "<Your username here>" +"!");
                } else {
                    ParseUser.logOut();
                    Toast.makeText(SignUpActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
                }
            }
        });
   

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   val user = ParseUser();
        // Set the user's username and password, which can be obtained by a forms
        user.setUsername("<Your username here>");
        user.setPassword("<Your password here>");
        user.signUpInBackground(SignUpCallback() {
            if (it == null) {
                showAlert("Successful Sign Up!", "Welcome" + "<Your username here>" + "!");
            } else {
                ParseUser.logOut();
                Toast.makeText(this, it.message, Toast.LENGTH_LONG).show();
            }
        });
   

   In the example project, this code is placed inside a SIGN UP button callback.
   Also, username and password are caught using Edit Texts.

3. It’s interesting to add an additional method to display Alert Dialogs and make the process look more professional. The method below do this:
   • Java
   • Kotlin

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   private void showAlert(String title,String message){
        AlertDialog.Builder builder = new AlertDialog.Builder(SignUpActivity.this)
                .setTitle(title)
                .setMessage(message)
                .setPositiveButton("OK", new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                        // don't forget to change the line below with the names of your Activities
                        Intent intent = new Intent(SignUpActivity.this, LogoutActivity.class);
                        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
                        startActivity(intent);
                    }
                });
        AlertDialog ok = builder.create();
        ok.show();
    }
   

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   private fun showAlert(title: String, message: String) {
        val builder = AlertDialog.Builder(this)
                .setTitle(title)
                .setMessage(message)
                .setPositiveButton("OK") { dialog, which ->
                    dialog.cancel()
                    // don't forget to change the line below with the names of your Activities
                    val intent = Intent(this, LogoutActivity::class.java)
                    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK or Intent.FLAG_ACTIVITY_NEW_TASK)
                    startActivity(intent)
                }
        val ok = builder.create()
        ok.show()
    }
   

Step 3 - Log in

Logging in creates a Session object, which points to the User logged in. If login is successful, ParseUser.getCurrentUser() returns a User object, and a Session object which created in the Dashboard. Otherwise, if the target username does not exist, or the password is wrong, it returns null.

The method used to perform the login action is ParseUser.logInInBackground(), which requires as many arguments as the strings of username and password, and may call a callback function.

Note: After signing up, login is performed automatically.

To make LoginActivity work, follow these steps:

1. Import into your LoginActivity, in addition to the dependencies imported in the Step 1:

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   import com.parse.LogInCallback;
   

2. To implement user login function, simply use the code:

   • Java
   • Kotlin

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   private void login(String username, String password) {
        progressDialog.show();
        ParseUser.logInInBackground(username, password, (parseUser, e) -> {
            progressDialog.dismiss();
            if (parseUser != null) {
                showAlert("Successful Login", "Welcome back " + username + " !");
            } else {
                ParseUser.logOut();
                Toast.makeText(LoginActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();
            }
        });
    }
   

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   fun login(username: String, password: String) {
        progressDialog?.show()
        ParseUser.logInInBackground(username,password) { parseUser: ParseUser?, parseException: ParseException? ->
            progressDialog?.dismiss()
            if (parseUser != null) {
                showAlert("Successful Login", "Welcome back " + username + " !")
            } else {
                ParseUser.logOut()
                if (parseException != null) {
                    Toast.makeText(this, parseException.message, Toast.LENGTH_LONG).show()
                }
            }
        }
    }
   

   In the example project, this code is placed inside a LOG IN button callback.
   Also, username and password are caught using Edit Texts.

   The method showAlert is the same that you added in the SignUpActivity, don’t forget to change its Intent arguments though.

Step 4 - Log Out

Logging out deletes the active Session object for the logged User. The method used to perform log out is ParseUser.logOutInBackground().

To implement user log out, simply use the code below, in the LogoutActivity:

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    ParseUser.logOutInBackground(e -> {
            progressDialog.dismiss();
            if (e == null)
                showAlert("So, you're going...", "Ok...Bye-bye then");
    });

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   ParseUser.logOutInBackground { e: ParseException? ->
            progressDialog!!.dismiss()
            if (e == null)
                showAlert("So, you're going...", "Ok...Bye-bye then")
    }

In the example project, this code is placed inside a LOG OUT button callback.

The method showAlert is the same that you added in the LoginActivity and SignUpActivity, don’t forget to change its Intent arguments though.

Step 5 - Test your app

1. Run your app and create a couple of users, also try logging in again after registering them.
2. Login at Back4App Website.
3. Find your app and click on Dashboard > Core > Browser > User.

At this point, you should see your users as displayed below:

Note: Using the codes displayed above, every time you log in with a user, a Session is opened in your Dashboard, but when the user logs out that particular Session ends. Also, whenever an unsuccessful login or sign up attempt occurs, the Session opened in Parse Server Dashboard is deleted.

It’s done!

Congrats ! Now you can log in, register or log out of your app using Parse Server core features through Back4App!