Android Google Sign-In

Requirements

Internet permission in Manifest
Application register with with firebase
Google sign-in library
Firebase library

Steps

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

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
Internet permission in manifest