Requirements

1. Internet permission in Manifest
2. Application register with with firebase
3. Google sign-in library
4. Firebase library

Steps

1. Declare internet permission in manifest

<uses-permission android:name="android.permission.INTERNET"/>

2. Now add google sign in library

implementation 'com.google.android.gms:play-services-auth:19.0.0'

3.  In MainActivity  on button click event we open google sign in dialogue from when we get user information’s like name, email, image Uri, user id at below show full code of sign in flow for google sign in.

• Sign-In Flow

• activty_main.xml File

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <com.google.android.gms.common.SignInButton
        android:id="@+id/google_sign_in"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

• MainActivity.java

  public class MainActivity extends AppCompatActivity {
  
      private static final String TAG = "MainActivity";
  
      private GoogleSignInClient signInClient;
      private final int SIGN_IN_REQ_CODE = 123;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          // if user already sign in using google account return not null otherwise return null
          if (getLastSignInAccount(this) != null){
              Intent intent = new Intent(this, UserActivity.class);
              startActivity(intent); // start user activity if user already login with gmail
              finish();
          }
  
          SignInButton googleSignIn = findViewById(R.id.google_sign_in);
          googleSignIn.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View v) {
                  GoogleSignInOptions signInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN).requestEmail().build();
                  signInClient = GoogleSignIn.getClient(MainActivity.this, signInOptions);
  
                  Intent signInIntent = signInClient.getSignInIntent();
                  startActivityForResult(signInIntent,SIGN_IN_REQ_CODE);
              }
          });
  
      }
  
      // return null if user is not sign in previously or return last account
      private GoogleSignInAccount getLastSignInAccount(Context context) {
          return GoogleSignIn.getLastSignedInAccount(context);
      }
  
  
      @Override
      protected void onActivityResult(int requestCode, int resultCode, Intent data) {
          super.onActivityResult(requestCode, resultCode, data);
  
          if (requestCode == SIGN_IN_REQ_CODE){
              if (data != null){
  
                  Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(data);
                  try {
                      GoogleSignInAccount account = task.getResult(ApiException.class);
                      String name = account.getDisplayName();
                      String email = account.getEmail();
  
                      // image can be null if user not set in their account
                      String imageUri = "";
                      if (account.getPhotoUrl() != null){
                          imageUri = account.getPhotoUrl().toString();
                      }
                      String userID = account.getId();
  
                      Log.d(TAG, "onActivityResult: user name"+name);
                      Log.d(TAG, "onActivityResult: user email"+email);
                      Log.d(TAG, "onActivityResult: user image uri"+imageUri);
                      Log.d(TAG, "onActivityResult: user id"+userID);
  
                      Intent intent = new Intent(MainActivity.this,UserActivity.class);
                      startActivity(intent);
                      finish();
  
                  } catch (ApiException e) {
                      Log.d("TAG", "handleSignInResult: "+e.getMessage());
                  }
              }
          }
      }
  
  }

   

• After complete successfully user sign-in we move user to next UserActivity

• Sign-Out Flow

  public class UserActivity extends AppCompatActivity {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_user);
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          getMenuInflater().inflate(R.menu.menu,menu);
          return true;
      }
  
      @Override
      public boolean onOptionsItemSelected(@NonNull MenuItem item) {
  
          if (item.getItemId() == R.id.sign_out){
              Intent logout = new Intent(UserActivity.this, MainActivity.class);
  
              GoogleSignInOptions signInOptions = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN).requestEmail().build();
              GoogleSignInClient signInClient = GoogleSignIn.getClient(UserActivity.this, signInOptions);
  
              signInClient.signOut()
                      .addOnCompleteListener(UserActivity.this, new OnCompleteListener<Void>() {
                          @Override
                          public void onComplete(@NonNull Task<Void> task) {
  
                          }
                      });
  
              startActivity(logout);
              finish();
          }
  
          return super.onOptionsItemSelected(item);
      }
  }

Note

•   For complete setup refer below GitHub project

Error Sources

1. Error code : 12500  (console conform email)
   • If you get this error code go to firebase console and Confirm your email in project setting in firebase console
2. Internet permission in manifest

Code Resource

• Replace project firebase json file with yours.

https://github.com/Rutvik-vision-403/Google_SignIn.git