How to use Firebase Phone and Google Authentication in Android.

Add Firebase to android studio

• Create a project on Firebase and then register your app with Firebase by entering the app’s package name in the Android package name field and then click register.
• Click Download google-services.json to obtain your Firebase Android config file (google-services.json) and paste into the module (app-level) directory of your app.
• Add the google-services-plugin to your Gradle files.
  In your module(project-level)

buildscript {

  repositories {
    // Check that you have the following line (if not, add it):
    google()  // Google's Maven repository
  }

  dependencies {
    // ...

    // Add the following line:
    classpath 'com.google.gms:google-services:4.3.3'  // Google Services plugin
  }
}

allprojects {
  // ...

  repositories {
    // Check that you have the following line (if not, add it):
    google()  // Google's Maven repository
    // ...
  }
}

In your module(app-level)

apply plugin: 'com.android.application'
// Add the following line:
apply plugin: 'com.google.gms.google-services'  // Google Services plugin

android {
  // ...
}

• Add dependencies into gradle.build(app-level)

implementation 'com.google.firebase:firebase-analytics:17.2.2'    implementation 'com.firebaseui:firebase-ui-auth:6.2.0'    implementation 'com.google.firebase:firebase-auth:19.3.0'

Check user is logged in or not

if (FirebaseAuth.getInstance().getCurrentUser()==null){ 
 //user is not logged in            
}      
else {            
 //User is logged in                       
 FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();                   }

Add sign-in and sign out on the button

buttonVariable.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        if (FirebaseAuth.getInstance().getCurrentUser() == null){
            showLogin();
            //Toast.makeText(OnBoarding.this, "You are logged in", Toast.LENGTH_SHORT).show();
        }
        else{
            signout();
        }
    }
});

private void showLogin() {
        List<AuthUI.IdpConfig> providers = Arrays.asList(
                //    new AuthUI.IdpConfig.PhoneBuilder().build(),
                new AuthUI.IdpConfig.GoogleBuilder().build()
        );

// Create and launch sign-in intent
        startActivityForResult(
                AuthUI.getInstance()
                        .createSignInIntentBuilder()
                        .setAvailableProviders(providers)
                        .build(),
                RC_SIGN_IN);
    }

private void signout() {
    AuthUI.getInstance()
            .signOut(this)
            .addOnCompleteListener(new OnCompleteListener<Void>() {
                public void onComplete(@NonNull Task<Void> task) {
                    // User logged out, updare data
                    Toast.makeText(OnBoarding.this, "Sign out Successfully", Toast.LENGTH_SHORT).show();

                }
            });
}

At last, overwrite the onActivityResult method

@Override
protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if (requestCode == RC_SIGN_IN) {
        IdpResponse response = IdpResponse.fromResultIntent(data);

        if (resultCode == RESULT_OK) {
            // Successfully signed in
            FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
            Toast.makeText(this, "Sign In Successful", Toast.LENGTH_SHORT).show();

            Intent intent = new Intent(OnBoarding.this, Dashboard.class);
            startActivity(intent);
            finish();

            // ...
        } else {
            // Sign in failed. If response is null the user canceled the
            Toast.makeText(this, "Sign In failed", Toast.LENGTH_SHORT).show();
        }
    }
}

Congratulations, Firebase Phone and Google Authentication are ready to use.

Resources

1. https://firebase.google.com/
2. https://developers.google.com/android/guides/google-services-plugin

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