How to do it...

Now, let's see how we can make the functionality work:

  1. Declare the FirebaseAuth reference, plus add another variable that we will need later on:
     FirebaseAuth auth;      private static final int RC_SIGN_IN = 17;
  1. Now, inside your onCreate method, add the following code:
     auth = FirebaseAuth.getInstance();      if(auth.getCurrentUser() != null) {          Log.d("Auth", "Logged in successfully");      } else {          startActivityForResult(            AuthUI.getInstance()             .createSignInIntentBuilder()              .setAvailableProviders(               Arrays.asList(new                 AuthUI.IdpConfig.Builder(                                                                  AuthUI.EMAIL_PROVIDER).build())).build(),                     RC_SIGN_IN);findViewById(R.id.logoutBtn)        .setOnClickListener(this);
  1. Now, in your activity, implement the View.OnClick listener. So your class will look ...

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