[go_router] Added top level onEnter callback.

Added onEnter callback to enable route interception and demonstrate usage in example.

packages/go_router/CHANGELOG.md

@@ -1,6 +1,7 @@
 ## NEXT
 
-* Updates minimum supported SDK version to Flutter 3.22/Dart 3.4.
+* Updated the minimum supported SDK version to Flutter 3.22/Dart 3.4.
+* Added new top level `onEnter` callback for controlling incoming route navigation.
 
 ## 14.6.2
 

packages/go_router/example/lib/top_level_on_enter.dart

@@ -0,0 +1,154 @@
+// Copyright 2013 The Flutter Authors.
+// Use of this source code is governed by a BSD-style license
+// that can be found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:go_router/go_router.dart';
+
+void main() => runApp(const App());
+
+/// The main application widget.
+class App extends StatelessWidget {
+  /// Constructs an [App].
+  const App({super.key});
+
+  /// The title of the app.
+  static const String title = 'GoRouter Example: Top-level onEnter';
+
+  @override
+  Widget build(BuildContext context) => MaterialApp.router(
+        routerConfig: GoRouter(
+          initialLocation: '/home',
+
+          /// A callback invoked for every route navigation attempt.
+          ///
+          /// If the callback returns `false`, the navigation is blocked.
+          /// Use this to handle authentication, referrals, or other route-based logic.
+          onEnter: (BuildContext context, GoRouterState state) {
+            // Save the referral code (if provided) and block navigation to the /referral route.
+            if (state.uri.path == '/referral') {
+              saveReferralCode(context, state.uri.queryParameters['code']);
+              return false;
+            }
+
+            return true; // Allow navigation for all other routes.
+          },
+
+          /// The list of application routes.
+          routes: <GoRoute>[
+            GoRoute(
+              path: '/login',
+              builder: (BuildContext context, GoRouterState state) =>
+                  const LoginScreen(),
+            ),
+            GoRoute(
+              path: '/home',
+              builder: (BuildContext context, GoRouterState state) =>
+                  const HomeScreen(),
+            ),
+            GoRoute(
+              path: '/settings',
+              builder: (BuildContext context, GoRouterState state) =>
+                  const SettingsScreen(),
+            ),
+          ],
+        ),
+        title: title,
+      );
+}
+
+/// The login screen widget.
+class LoginScreen extends StatelessWidget {
+  /// Constructs a [LoginScreen].
+  const LoginScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(title: const Text(App.title)),
+        body: Center(
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              ElevatedButton(
+                onPressed: () => context.go('/home'),
+                child: const Text('Go to Home'),
+              ),
+              ElevatedButton(
+                onPressed: () => context.go('/settings'),
+                child: const Text('Go to Settings'),
+              ),
+            ],
+          ),
+        ),
+      );
+}
+
+/// The home screen widget.
+class HomeScreen extends StatelessWidget {
+  /// Constructs a [HomeScreen].
+  const HomeScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(title: const Text(App.title)),
+        body: Center(
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              ElevatedButton(
+                onPressed: () => context.go('/login'),
+                child: const Text('Go to Login'),
+              ),
+              ElevatedButton(
+                onPressed: () => context.go('/settings'),
+                child: const Text('Go to Settings'),
+              ),
+              ElevatedButton(
+                // This would typically be triggered by an incoming deep link.
+                onPressed: () => context.go('/referral?code=12345'),
+                child: const Text('Save Referral Code'),
+              ),
+            ],
+          ),
+        ),
+      );
+}
+
+/// The settings screen widget.
+class SettingsScreen extends StatelessWidget {
+  /// Constructs a [SettingsScreen].
+  const SettingsScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(title: const Text(App.title)),
+        body: Center(
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              ElevatedButton(
+                onPressed: () => context.go('/login'),
+                child: const Text('Go to Login'),
+              ),
+              ElevatedButton(
+                onPressed: () => context.go('/home'),
+                child: const Text('Go to Home'),
+              ),
+            ],
+          ),
+        ),
+      );
+}
+
+/// Saves a referral code.
+///
+/// Displays a [SnackBar] with the referral code for demonstration purposes.
+/// Replace this with real referral handling logic.
+void saveReferralCode(BuildContext context, String? code) {
+  if (code != null) {
+    // Here you can implement logic to save the referral code as needed.
+    ScaffoldMessenger.of(context).showSnackBar(
+      SnackBar(content: Text('Referral code saved: $code')),
+    );
+  }
+}

packages/go_router/lib/src/configuration.dart

@@ -20,13 +20,17 @@ import 'state.dart';
 typedef GoRouterRedirect = FutureOr<String?> Function(
     BuildContext context, GoRouterState state);
 
+/// The signature of the onEnter callback.
+typedef OnEnter = bool Function(BuildContext context, GoRouterState state);
+
 /// The route configuration for GoRouter configured by the app.
 class RouteConfiguration {
   /// Constructs a [RouteConfiguration].
   RouteConfiguration(
     this._routingConfig, {
     required this.navigatorKey,
     this.extraCodec,
+    this.onEnter,
   }) {
     _onRoutingTableChanged();
     _routingConfig.addListener(_onRoutingTableChanged);
@@ -246,6 +250,35 @@ class RouteConfiguration {
   ///    example.
   final Codec<Object?, Object?>? extraCodec;
 
+  /// A callback invoked for every incoming route before it is processed.
+  ///
+  /// This callback allows you to control navigation by inspecting the incoming
+  /// route and conditionally preventing the navigation. If the callback returns
+  /// `true`, the GoRouter proceeds with the regular navigation and redirection
+  /// logic. If the callback returns `false`, the navigation is canceled.
+  ///
+  /// When a deep link opens the app and `onEnter` returns `false`,  GoRouter
+  /// will automatically redirect to the initial route or '/'.
+  ///
+  /// Example:
+  /// ```dart
+  /// final GoRouter router = GoRouter(
+  ///   routes: [...],
+  ///   onEnter: (BuildContext context, Uri uri) {
+  ///     if (uri.path == '/login' && isUserLoggedIn()) {
+  ///       return false; // Prevent navigation to /login
+  ///     }
+  ///     if (uri.path == '/referral') {
+  ///       // Save the referral code and prevent navigation
+  ///       saveReferralCode(uri.queryParameters['code']);
+  ///       return false;
+  ///     }
+  ///     return true; // Allow navigation
+  ///   },
+  /// );
+  /// ```
+  final OnEnter? onEnter;
+
   final Map<String, String> _nameToPath = <String, String>{};
 
   /// Looks up the url location by a [GoRoute]'s name.