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Flutter login using Facebook authentication

Amey Sunu

Getting started

To begin, you need to have a Facebook account. Then, go to pub.dev, get the flutter_facebook_login package, and add it to your pubspec.yaml. Now, this tutorial will be split in half, with one section for Android and another one for iOS. The main reason is that the installation of Facebook SDK will be different for both users.

Android installation

  • Visit Facebook for Developer’s Android Quickstart and complete all Steps 1-6from installation and configuring up to development to releasing Key hashes. The steps after that are mostly for Kotlin and Java, so until Step 6, everything will be familiar.

  • Create a new file under android/app/src/main/res/values named strings.xml and add the following values:

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">App Name</string>
    <string name="facebook_app_id">XXXXXXXXXXXX</string>
    <string name="fb_login_protocol_scheme">fbXXXXXXXXXXXX</string>
</resources>

Replace the app name, Facebook App ID, and your Facebook Login Protocol Scheme with your retrieved details from the Facebook Developer Console.

iOS installation

Since the AppDelegate connection is a part of Swift and SwiftUI, we do not need that.

For any issues and troubleshooting, visit the pub.dev page for the package.

Now, import the package into your dart file, and create a login function:

void fbLogin() async {
    var facebookLogin = FacebookLogin();
    var facebookLoginResult = await facebookLogin.logInWithReadPermissions(['email']);
     switch (facebookLoginResult.status) {
      case FacebookLoginStatus.error:
        print("Error");
        onLoginStatusChanged(false);
        break;
      case FacebookLoginStatus.cancelledByUser:
        print("CancelledByUser");
        onLoginStatusChanged(false);
        break;
      case FacebookLoginStatus.loggedIn:
        print("LoggedIn");
        onLoginStatusChanged(true);
        break;
    }
  }

The onLoginStatusChanged is used to update the UI using setState() when the user logs in to handle the UI a little better:

bool isLoggedIn = false;

  void onLoginStatusChanged(bool isLoggedIn) {
    setState(() {
      this.isLoggedIn = isLoggedIn;
    });
  }

Now, simply go ahead and call the fbLogin() function inside of a buttonwill be your Facebook signup button. This should prompt you to a Facebook signup.

Retrieving user image and name

Once signed in, you can also get your user image and name:

var userDetails = await http.get(Uri.parse('https://graph.facebook.com/v2.12/me?fields=name,first_name,last_name,email,picture.height(200)&access_token=${facebookLoginResult.accessToken.token}'));

Note: http is imported from the http package that is available here. This package allows users to create HTTP requests, so you can import it as the following: import 'package:http/http.dart' as HTTP;

Now, parse the response and decode the JSON value:

var profile = json.decode(graphResponse.body);
print(profile.toString());

Once you print the profile, you’ll be able to see a response inside your console. Within this response, you can see parameters like the name.

If you want to use the name, simply go ahead and use it as:

Text(profile['name'])

For global access, create a variable, assign it to profile, and check out for null safety to ensure there is no user-end crash.

To access the image, you can use NetworkImage and parse the URL as:

profile['picture']['data']['url']

If you need any assistance, check out the example code by the package maintainers here.

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