Google APIs

The Google APIs package exposes dozens of Google services that you can use from Dart projects.

This page describes how to use APIs that interact with end-user data by using Google authentication.

Examples of user-data APIs include Calendar, Gmail, YouTube, and Firebase.

To add authentication to Firebase explicitly, check out the Add a user authentication flow to a Flutter app using FirebaseUI codelab and the Get Started with Firebase Authentication on Flutter docs.

To use Google APIs, follow these steps:

1. Pick the desired API
2. Enable the API
3. Authenticate user with the required scopes
4. Obtain an authenticated HTTP client
5. Create and use the desired API class

The documentation for package:googleapis lists each API as a separate Dart library&emdash;in a name_version format. Check out youtube_v3 as an example.

Each library might provide many types, but there is one root class that ends in Api. For YouTube, it's YouTubeApi.

Not only is the Api class the one you need to instantiate (see step 3), but it also exposes the scopes that represent the permissions needed to use the API. For example, the Constants section of the YouTubeApi class lists the available scopes. To request access to read (but not write) an end-users YouTube data, authenticate the user with youtubeReadonlyScope.

/// Provides the `YouTubeApi` class.
import 'package:googleapis/youtube/v3.dart';

To use Google APIs you must have a Google account and a Google project. You also need to enable your desired API.

This example enables YouTube Data API v3. For details, see the getting started instructions.

Use the google_sign_in package to authenticate users with their Google identity. Configure signin for each platform you want to support.

/// Provides the `GoogleSignIn` class
import 'package:google_sign_in/google_sign_in.dart';

When instantiating the GoogleSignIn class, provide the desired scopes as discussed in the previous section.

final _googleSignIn = GoogleSignIn(
  scopes: <String>[YouTubeApi.youtubeReadonlyScope],
);

Follow the instructions provided by package:google_sign_in to allow a user to authenticate.

Once authenticated, you must obtain an authenticated HTTP client.

The extension_google_sign_in_as_googleapis_auth package provides an extension method on GoogleSignIn called authenticatedClient.

import 'package:extension_google_sign_in_as_googleapis_auth/extension_google_sign_in_as_googleapis_auth.dart';

Add a listener to onCurrentUserChanged and when the event value isn't null, you can create an authenticated client.

var httpClient = (await _googleSignIn.authenticatedClient())!;

This Client instance includes the necessary credentials when invoking Google API classes.

Use the API to create the desired API type and call methods. For instance:

var youTubeApi = YouTubeApi(httpClient);

var favorites = await youTubeApi.playlistItems.list(
  ['snippet'],
  playlistId: 'LL', // Liked List
);

You might want to check out the following:

• The extension_google_sign_in_as_googleapis_auth example is a working implementation of the concepts described on this page.