Set up app links for Android

Deep linking is a mechanism for launching an app with a URI. This URI contains scheme, host, and path, and opens the app to a specific screen.

A app link is a type of deep link that uses http or https and is exclusive to Android devices.

Setting up app links requires one to own a web domain. Otherwise, consider using Firebase Hosting or GitHub Pages as a temporary solution.

1. Customize a Flutter application

Write a Flutter app that can handle an incoming URL. This example uses the go_router package to handle the routing. The Flutter team maintains the go_router package. It provides a simple API to handle complex routing scenarios.

1. To create a new application, type flutter create <app-name>:

    $ flutter create deeplink_cookbook
   

2. To include go_router package in your app, add a dependency for go_router to the project:

   To add the go_router package as a dependency, run flutter pub add:

    $ flutter pub add go_router
   

3. To handle the routing, create a GoRouter object in the main.dart file:

   import 'package:flutter/material.dart';
    import 'package:go_router/go_router.dart';
   
    void main() => runApp(MaterialApp.router(routerConfig: router));
   
    /// This handles '/' and '/details'.
    final router = GoRouter(
      routes: [
        GoRoute(
          path: '/',
          builder: (_, __) => Scaffold(
            appBar: AppBar(title: const Text('Home Screen')),
          ),
          routes: [
            GoRoute(
              path: 'details',
              builder: (_, __) => Scaffold(
                appBar: AppBar(title: const Text('Details Screen')),
              ),
            ),
          ],
        ),
      ],
    );

2. Modify AndroidManifest.xml

1. Open the Flutter project with VS Code or Android Studio.
2. Navigate to android/app/src/main/AndroidManifest.xml file.

3. Add the following metadata tag and intent filter inside the <activity> tag with .MainActivity.

   Replace example.com with your own web domain.

    <meta-data android:name="flutter_deeplinking_enabled" android:value="true" />
    <intent-filter android:autoVerify="true">
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data android:scheme="http" android:host="example.com" />
        <data android:scheme="https" />
    </intent-filter>
   

3. Hosting assetlinks.json file

Host an assetlinks.json file in using a web server with a domain that you own. This file tells the mobile browser which Android application to open instead of the browser. To create the file, get the package name of the Flutter app you created in the previous step and the sha256 fingerprint of the signing key you will be using to build the APK.

Package name

Locate the package name in AndroidManifest.xml, the package property under <manifest> tag. Package names are usually in the format of com.example.*.

sha256 fingerprint

The process might differ depending on how the apk is signed.

Using google play app signing

You can find the sha256 fingerprint directly from play developer console. Open your app in the play console, under Release> Setup > App Integrity> App Signing tab:

Using local keystore

If you are storing the key locally, you can generate sha256 using the following command:

keytool -list -v -keystore <path-to-keystore>

assetlinks.json

The hosted file should look similar to this:

[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "com.example.deeplink_cookbook",
    "sha256_cert_fingerprints":
    ["FF:2A:CF:7B:DD:CC:F1:03:3E:E8:B2:27:7C:A2:E3:3C:DE:13:DB:AC:8E:EB:3A:B9:72:A1:0E:26:8A:F5:EC:AF"]
  }
}]

1. Set the package_name value to your Android application ID.

2. Set sha256_cert_fingerprints to the value you got from the previous step.

3. Host the file at a URL that resembles the following: <webdomain>/.well-known/assetlinks.json

4. Verify that your browser can access this file.

Testing

You can use a real device or the Emulator to test an app link, but first make sure you have executed flutter run at least once on the devices. This ensures that the Flutter application is installed.

To test only the app setup, use the adb command:

adb shell 'am start -a android.intent.action.VIEW \
    -c android.intent.category.BROWSABLE \
    -d "http://<web-domain>/details"' \
    <package name>

To test both web and app setup, you must click a link directly through web browser or another app. One way is to create a Google Doc, add the link, and tap on it.

If everything is set up correctly, the Flutter application launches and displays the details screen:

Appendix

Source code: deeplink_cookbook