User Login in Android using Back4App - GeeksforGeeks

06 Nov, 2021
We have seen implementing User Registration in Android using Back4App. In that article, we have implemented User Registration in our App. In this article, we will take a look at the implementation of User Login in our Android App. 
We will be building a simple application in which we will be displaying a user login form in Android App and using this login form we will allow our user to login inside our application. A sample video is given below to get an idea about what we are going to do in this article. Note that we are going to implement this project using the Java language. 
This article is the continuation of User Registration in Android using Back4App.
Step 1: Working with the activity_main.xml file
Navigate to the app > res > layout > activity_main.xml and add the below code to that file. Below is the code for the activity_main.xml file. 
XML
<?xml version="1.0" encoding="utf-8"?><RelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".MainActivity">     <!--text view for heading-->    <TextView        android:id="@+id/idTVHeader"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_marginTop="30dp"        android:gravity="center_horizontal"        android:padding="5dp"        android:text="Welcome to Geeks for Geeks \n Login Form"        android:textAlignment="center"        android:textColor="@color/purple_700"        android:textSize="18sp" />     <!--edit text for user name-->    <EditText        android:id="@+id/idEdtUserName"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/idTVHeader"        android:layout_marginStart="10dp"        android:layout_marginTop="50dp"        android:layout_marginEnd="10dp"        android:hint="Enter UserName"        android:inputType="textEmailAddress" />     <!--edit text for user password-->    <EditText        android:id="@+id/idEdtPassword"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/idEdtUserName"        android:layout_marginStart="10dp"        android:layout_marginTop="20dp"        android:layout_marginEnd="10dp"        android:hint="Enter Password"        android:inputType="textPassword" />     <!--button to register our new user-->    <Button        android:id="@+id/idBtnLogin"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/idEdtPassword"        android:layout_marginStart="10dp"        android:layout_marginTop="20dp"        android:layout_marginEnd="10dp"        android:text="Login"        android:textAllCaps="false" /> </RelativeLayout>
 Step 2: Creating a new activity to redirect our user after registration
Navigate to the app > java > your app’s package name > Right-click on it > New > Empty Activity and name it as HomeActivity. or you may also refer to this article How to Create New Activity in Android Studio?
Step 3: Working with the activity_home.xml file
Navigate to the app > res > layout > activity_home.xml file and add the below code to it.  
XML
<?xml version="1.0" encoding="utf-8"?><RelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".HomeActivity">         <!--text view for displaying heading-->    <TextView        android:id="@+id/idTVHeader"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_centerInParent="true"        android:gravity="center_horizontal"        android:text="Welcome back again to Geeks for Geeks"        android:textAlignment="center"        android:textColor="@color/purple_700"        android:textSize="18sp" />         <!--text view for displaying user name-->    <TextView        android:id="@+id/idTVUserName"        android:layout_width="match_parent"        android:layout_height="wrap_content"        android:layout_below="@id/idTVHeader"        android:layout_centerInParent="true"        android:layout_marginTop="20dp"        android:gravity="center_horizontal"        android:text="UserName"        android:textAlignment="center"        android:textColor="@color/purple_700"        android:textSize="25sp" />     <!--button for making user log out-->    <Button        android:id="@+id/idBtnLogout"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_below="@id/idTVUserName"        android:layout_centerInParent="true"        android:layout_marginTop="10dp"        android:text="LogOut"        android:textAllCaps="false" />     </RelativeLayout>
 Step 4: Working with the HomeActivity.java file
Navigate to the app > java > your app’s package name > HomeActivity.java file and add the below code to it. Comments are added inside the code to understand the code in more detail. 
Java
import android.content.Intent;import android.os.Bundle;import android.view.View;import android.widget.Button;import android.widget.TextView;import android.widget.Toast; import androidx.appcompat.app.AppCompatActivity; import com.parse.ParseUser; public class HomeActivity extends AppCompatActivity {     // creating a variable    // for our text view..    private TextView userNameTV;         // button for logout    private Button logoutBtn;     @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_home);        logoutBtn = findViewById(R.id.idBtnLogout);                 // initializing our variables        userNameTV = findViewById(R.id.idTVUserName);                 // getting data from intent.        String name = getIntent().getStringExtra("username");                 // setting data to our text view.        userNameTV.setText(name);                // initializing click listener for logout button        logoutBtn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                // calling a method to logout our user.                ParseUser.logOutInBackground(e -> {                    if (e == null) {                        Toast.makeText(HomeActivity.this, "User Logged Out", Toast.LENGTH_SHORT).show();                        Intent i = new Intent(HomeActivity.this, MainActivity.class);                        startActivity(i);                        finish();                    }                });            }        });    }}
 Step 5: Working with the MainActivity.java file
Go to the MainActivity.java file and refer to the following code. Below is the code for the MainActivity.java file. Comments are added inside the code to understand the code in more detail. 
Java
import android.content.Intent;import android.os.Bundle;import android.text.TextUtils;import android.view.View;import android.widget.Button;import android.widget.EditText;import android.widget.Toast; import androidx.appcompat.app.AppCompatActivity; import com.parse.ParseUser; public class MainActivity extends AppCompatActivity {         // creating variables for our edit text and buttons.    private EditText userNameEdt, passwordEdt;    private Button loginBtn;     @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                 // initializing our edit text  and buttons.        userNameEdt = findViewById(R.id.idEdtUserName);        passwordEdt = findViewById(R.id.idEdtPassword);        loginBtn = findViewById(R.id.idBtnLogin);                 // adding on click listener for our button.        loginBtn.setOnClickListener(new View.OnClickListener() {            @Override            public void onClick(View v) {                                 // on below line we are getting data from our edit text.                String userName = userNameEdt.getText().toString();                String password = passwordEdt.getText().toString();                                 // checking if the entered text is empty or not.                if (TextUtils.isEmpty(userName) && TextUtils.isEmpty(password)) {                    Toast.makeText(MainActivity.this, "Please enter user name and password", Toast.LENGTH_SHORT).show();                }                                 // calling a method to login our user.                loginUser(userName, password);            }        });    }     private void loginUser(String userName, String password) {        // calling a method to login a user.        ParseUser.logInInBackground(userName, password, (parseUser, e) -> {            // after login checking if the user is null or not.            if (parseUser != null) {                // if the user is not null then we will display a toast message                // with user login and passing that user to new activity.                Toast.makeText(this, "Login Successful ", Toast.LENGTH_SHORT).show();                Intent i = new Intent(MainActivity.this, HomeActivity.class);                i.putExtra("username", userName);                startActivity(i);            } else {                // display an toast message when user logout of the app.                ParseUser.logOut();                Toast.makeText(MainActivity.this, e.getMessage(), Toast.LENGTH_LONG).show();            }        });    }}
 Now run your app and see the output of the app:
Output:  
Check out the project on the below link: https://github.com/ChaitanyaMunje/GFG-Back4App/tree/LoginForm
 
kalrap615
Android
Java
Java
Android
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