Introduction

Deep links let your app open specific content from URLs or custom schemes. For Flutter mobile development, implementing deep links end to end requires configuration on Android and iOS, plus Flutter-side handling that is robust to cold starts and background events. This tutorial shows a practical, code-forward approach: App Links/Universal Links for web-hosted deep linking and custom schemes as a fallback. You will learn manifest and entitlements setup, how to listen for links in Flutter, and how to test on devices and emulators.

Understanding Deep Links

There are two common deep link types: custom URL schemes (myapp://path) and platform-managed links (Android App Links and iOS Universal Links using https). Platform-managed links are preferred because they are secure and allow opening the app without prompting when the domain is verified. For mobile development with flutter, plan your link patterns, choose host names and path prefixes, and host the verification files (assetlinks.json for Android, apple-app-site-association for iOS) at the root of the domain with correct content types.

Key goals:

• Use https links for verified behavior.

• Support fallback to custom schemes for older OS versions where necessary.

• Handle both initialUri (cold start) and link stream (runtime).

Configuring Android

1. AndroidManifest.xml: add an intent-filter inside the that launches your Flutter activity. Use scheme https, host, and pathPrefix or pathPattern. For App Links add android:autoVerify="true".

2. Hosting: place a digital asset links file at https://yourdomain/.well-known/assetlinks.json listing your app's package name and SHA256 certificate fingerprints. The file must be served with content-type application/json.

3. Custom scheme fallback: also declare an intent-filter for a custom scheme if you want myapp:// style links.

Example manifest fragment (conceptual):

• intent-filter with action VIEW, categories DEFAULT and BROWSABLE, data scheme https host example.com

Verify with adb after installing:

• adb shell am start -a android.intent.action.VIEW -d https://example.com/path com.example.yourapp

If autoVerify fails, the system will not open links automatically; ensure assetlinks.json matches exactly the app signing certificate.

Configuring iOS

1. Associated Domains capability: enable in Xcode and add an entitlement entry under Associated Domains: applinks:example.com.

2. Hosting: create an apple-app-site-association JSON at https://example.com/apple-app-site-association (no .json extension). Serve as application/json and include your app's appID in the applinks section.

3. Custom URL scheme: add a URL type in Info.plist for scheme-based linking as fallback.

Notes: Universal Links open the app without asking only if the AASA file is valid and the app has the entitlement. Test with the simulator using xcrun simctl openurl.

Handling Links In Flutter

Use a dedicated package such as uni_links to manage both the initial link and the stream of incoming links. Handle three cases: cold start (getInitialUri), resume from background (getInitialUri may return non-null), and foreground link events (uriLinkStream). Always validate the Uri and route within your app.

Example initialization in main.dart:

import 'package:flutter/material.dart';
import 'package:uni_links/uni_links.dart';
<p>void main() => runApp(MyApp());</p>

Listener pattern (concise example):

// inside a State class
@override
void initState() {
  super.initState();
  _initDeepLinkHandling();
}
<p>Future<void> _initDeepLinkHandling() async {<br>final initial = await getInitialUri();<br>if (initial != null) _handleUri(initial);<br>uriLinkStream.listen((Uri? uri) { if (uri != null) _handleUri(uri); });<br>}</p>

Routing: convert the incoming Uri to a route name or directly push a page with parsed parameters. Do not assume a single entry point; check whether the navigator is ready (use a navigatorKey) and queue the deep link until Flutter finishes bootstrapping.

Testing in Flutter: use adb and simctl to open https links and observe navigation. For web-hosted links test that the verification files are reachable over HTTPS and have the right MIME type.

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Conclusion

End-to-end deep linking on Android and iOS requires coordinated changes: domain-hosted verification files, platform manifest or entitlements changes, and Flutter code that handles both initial and runtime link events. Use App Links and Universal Links whenever possible for security and user experience, and fall back to custom schemes if needed. With uni_links or similar packages and careful testing via adb and simctl, you can implement reliable deep linking in your flutter mobile development projects.