flutter-setup-declarative-routing

What this skill does

# Implementing Routing and Deep Linking

## Contents
- [Core Concepts](#core-concepts)
- [Workflow: Initializing the Application and Router](#workflow-initializing-the-application-and-router)
- [Workflow: Configuring Platform Deep Linking](#workflow-configuring-platform-deep-linking)
- [Workflow: Implementing Nested Navigation](#workflow-implementing-nested-navigation)
- [Examples](#examples)

## Core Concepts

Use the `go_router` package for declarative routing in Flutter. It provides a robust API for complex routing scenarios, deep linking, and nested navigation. 

- **GoRouter**: The central configuration object defining the application's route tree.
- **GoRoute**: A standard route mapping a URL path to a Flutter screen.
- **ShellRoute / StatefulShellRoute**: Wraps child routes in a persistent UI shell (e.g., a `BottomNavigationBar`). `StatefulShellRoute` maintains the state of parallel navigation branches.
- **Path URL Strategy**: Removes the default `#` fragment from web URLs, essential for clean deep linking across platforms.

## Workflow: Initializing the Application and Router

Follow this workflow to bootstrap a new Flutter application with `go_router` and configure the root routing mechanism.

### Task Progress
- [ ] Create the Flutter application.
- [ ] Add the `go_router` dependency.
- [ ] Configure the URL strategy for web/deep linking.
- [ ] Implement the `GoRouter` configuration.
- [ ] Bind the router to `MaterialApp.router`.

### 1. Scaffold the Application
Run the following commands to create the app and add the required routing package:
```bash
flutter create <app-name>
cd <app-name>
flutter pub add go_router
```

### 2. Configure the Router
Define a top-level `GoRouter` instance. Handle authentication or state-based routing using the `redirect` parameter.

```dart
import 'package:flutter/material.dart';
import 'package:go_router/go_router.dart';
import 'package:flutter_web_plugins/url_strategy.dart';

void main() {
  // Use path URL strategy to remove the '#' from web URLs
  usePathUrlStrategy();
  runApp(const MyApp());
}

final GoRouter _router = GoRouter(
  initialLocation: '/',
  routes: [
    GoRoute(
      path: '/',
      builder: (context, state) => const HomeScreen(),
      routes: [
        GoRoute(
          path: 'details/:id',
          builder: (context, state) => DetailsScreen(id: state.pathParameters['id']!),
        ),
      ],
    ),
  ],
  errorBuilder: (context, state) => ErrorScreen(error: state.error),
);

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp.router(
      routerConfig: _router,
      title: 'Routing App',
    );
  }
}
```

## Workflow: Configuring Platform Deep Linking

Configure the native platforms to intercept specific URLs and route them into the Flutter application.

### Task Progress
- [ ] Determine target platforms (iOS, Android, or both).
- [ ] Apply conditional configuration for Android (Manifest + Asset Links).
- [ ] Apply conditional configuration for iOS (Plist + Entitlements + AASA).
- [ ] Run validator -> review errors -> fix.

### If configuring for Android:
1. **Modify `AndroidManifest.xml`**: Add the intent filter inside the `<activity>` tag for `.MainActivity`.
```xml
<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="yourdomain.com" />
    <data android:scheme="https" />
</intent-filter>
```
2. **Host `assetlinks.json`**: Serve the following JSON at `https://yourdomain.com/.well-known/assetlinks.json`.
```json
[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "com.yourcompany.yourapp",
    "sha256_cert_fingerprints": ["YOUR_SHA256_FINGERPRINT"]
  }
}]
```

### If configuring for iOS:
1. **Modify `Info.plist`**: Opt-in to Flutter's default deep link handler. 
*Note: If using a third-party deep linking plugin (e.g., `app_links`), set this to `NO` to prevent conflicts.*
```xml
<key>FlutterDeepLinkingEnabled</key>
<true/>
```
2. **Modify `Runner.entitlements`**: Add the associated domain.
```xml
<key>com.apple.developer.associated-domains</key>
<array>
  <string>applinks:yourdomain.com</string>
</array>
```
3. **Host `apple-app-site-association`**: Serve the following JSON (without a `.json` extension) at `https://yourdomain.com/.well-known/apple-app-site-association`.
```json
{
  "applinks": {
    "apps": [],
    "details": [{
      "appIDs": ["TEAM_ID.com.yourcompany.yourapp"],
      "paths": ["*"],
      "components": [{"/": "/*"}]
    }]
  }
}
```

### Validation Loop
Run validator -> review errors -> fix.
- **Android**: Test using ADB.
  ```bash
  adb shell 'am start -a android.intent.action.VIEW -c android.intent.category.BROWSABLE -d "https://yourdomain.com/details/123"' com.yourcompany.yourapp
  ```
- **iOS**: Test using `xcrun` on a booted simulator.
  ```bash
  xcrun simctl openurl booted https://yourdomain.com/details/123
  ```

## Workflow: Implementing Nested Navigation

Use `StatefulShellRoute` to implement persistent UI shells (like a bottom navigation bar) that maintain the state of their child routes.

### Task Progress
- [ ] Define `StatefulShellRoute.indexedStack` in the `GoRouter` configuration.
- [ ] Create `StatefulShellBranch` instances for each navigation tab.
- [ ] Implement the shell widget using `StatefulNavigationShell`.

```dart
final GoRouter _router = GoRouter(
  initialLocation: '/home',
  routes: [
    StatefulShellRoute.indexedStack(
      builder: (context, state, navigationShell) {
        return ScaffoldWithNavBar(navigationShell: navigationShell);
      },
      branches: [
        StatefulShellBranch(
          routes: [
            GoRoute(
              path: '/home',
              builder: (context, state) => const HomeScreen(),
            ),
          ],
        ),
        StatefulShellBranch(
          routes: [
            GoRoute(
              path: '/settings',
              builder: (context, state) => const SettingsScreen(),
            ),
          ],
        ),
      ],
    ),
  ],
);
```

## Examples

### High-Fidelity Shell Widget Implementation
Implement the UI shell that consumes the `StatefulNavigationShell` to handle branch switching.

```dart
class ScaffoldWithNavBar extends StatelessWidget {
  const ScaffoldWithNavBar({
    required this.navigationShell,
    super.key,
  });

  final StatefulNavigationShell navigationShell;

  void _goBranch(int index) {
    navigationShell.goBranch(
      index,
      // Support navigating to the initial location when tapping the active tab.
      initialLocation: index == navigationShell.currentIndex,
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: navigationShell,
      bottomNavigationBar: NavigationBar(
        selectedIndex: navigationShell.currentIndex,
        onDestinationSelected: _goBranch,
        destinations: const [
          NavigationDestination(icon: Icon(Icons.home), label: 'Home'),
          NavigationDestination(icon: Icon(Icons.settings), label: 'Settings'),
        ],
      ),
    );
  }
}
```

### Programmatic Navigation
Use the `context.go()` and `context.push()` extension methods provided by `go_router`.

```dart
// Replaces the current route stack with the target route (Declarative)
context.go('/details/123');

// Pushes the target route onto the existing stack (Imperative)
context.push('/details/123');

// Navigates using a named route and path parameters
context.goNamed('details', pathParameters: {'id': '123'});

// Pops the current route
context.pop();
```