05. Enabling Login

In this step you’ll implement the login feature for your users.

1. Open the file MainFragment.kt. In the MainFragment’s layout there is an auth_button, but it’s currently not setup to handle any user input yet. In onViewCreated(), add an onClickListener to auth_button to call launchSignInFlow().

MainFragment.kt

binding.authButton.setOnClickListener { launchSignInFlow() }

2. Look for the launchSignInFlow() method in MainFragment.kt that currently contains a TODO. Complete the launchSignInFlow() function by allowing users to register and sign in with their email address or Google account. If the user chooses to register with their email address, the email and password combination they create is unique for your app. That means they will be able to login to your app with the email address and password combination, but it doesn’t mean they can also login to any other Firebase supported app by default.

MainFragment.kt

private fun launchSignInFlow() {
   // Give users the option to sign in / register with their email or Google account.
   // If users choose to register with their email,
   // they will need to create a password as well.
   val providers = arrayListOf(
       AuthUI.IdpConfig.EmailBuilder().build(), AuthUI.IdpConfig.GoogleBuilder().build()

       // This is where you can provide more ways for users to register and 
       // sign in.
   )

   // Create and launch sign-in intent.
   // We listen to the response of this activity with the
   // SIGN_IN_REQUEST_CODE 
   startActivityForResult(
       AuthUI.getInstance()
           .createSignInIntentBuilder()
           .setAvailableProviders(providers)
           .build(),
       MainFragment.SIGN_IN_REQUEST_CODE
   )
}

3. In MainFragment.kt, you can listen for the result of the sign-in process by implementing the onActivityResult() method. Since you started the sign in process with SIGN_IN_REQUEST_CODE, you can also listen to the result of the sign in process by filtering for when SIGN_IN_REQUEST_CODE is passed back to onActivityResult(). Start by having some log statements to know whether the user has signed in successfully.

MainFragment.kt

override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
   super.onActivityResult(requestCode, resultCode, data)
   if (requestCode == SIGN_IN_REQUEST_CODE) {
       val response = IdpResponse.fromResultIntent(data)
       if (resultCode == Activity.RESULT_OK) {
           // User successfully signed in
           Log.i(TAG, "Successfully signed in user ${FirebaseAuth.getInstance().currentUser?.displayName}!")
       } else {
           // Sign in failed. If response is null the user canceled the
           // sign-in flow using the back button. Otherwise check
           // response.getError().getErrorCode() and handle the error.
           Log.i(TAG, "Sign in unsuccessful ${response?.error?.errorCode}")
       }
   }
}

4. Your app should now be able to handle registering and logging in users! Run the app and verify that tapping on the Login button now brings up the login screen. You can now sign in with your email address and a password, or with your Google account. There will be no change in the UI after you login (you’ll implement updating the UI in the next step), but if everything is working correctly, you should see the log message Successfully signed in user ${your name}! after you go through the registration flow. You can also go into the Firebase console and navigate to Develop > Authentication > Users to check that the app now has one registered user.