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lib/13/go/redirection.dart

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+// Copyright 2013 The Flutter Authors. All rights reserved.
+// 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';
+import 'package:provider/provider.dart';
+
+// This scenario demonstrates how to use redirect to handle a sign-in flow.
+//
+// The GoRouter.redirect method is called before the app is navigate to a
+// new page. You can choose to redirect to a different page by returning a
+// non-null URL string.
+
+/// The login information.
+class LoginInfo extends ChangeNotifier {
+  /// The username of login.
+  String get userName => _userName;
+  String _userName = '';
+
+  /// Whether a user has logged in.
+  bool get loggedIn => _userName.isNotEmpty;
+
+  /// Logs in a user.
+  void login(String userName) {
+    _userName = userName;
+    notifyListeners();
+  }
+
+  /// Logs out the current user.
+  void logout() {
+    _userName = '';
+    notifyListeners();
+  }
+}
+
+void main() => runApp(App());
+
+/// The main app.
+class App extends StatelessWidget {
+  /// Creates an [App].
+  App({super.key});
+
+  final LoginInfo _loginInfo = LoginInfo();
+
+  /// The title of the app.
+  static const String title = 'GoRouter Example: Redirection';
+
+  // add the login info into the tree as app state that can change over time
+  @override
+  Widget build(BuildContext context) => ChangeNotifierProvider<LoginInfo>.value(
+        value: _loginInfo,
+        child: MaterialApp.router(
+          routerConfig: _router,
+          title: title,
+          debugShowCheckedModeBanner: false,
+        ),
+      );
+
+  late final GoRouter _router = GoRouter(
+    routes: <GoRoute>[
+      GoRoute(
+        path: '/',
+        builder: (BuildContext context, GoRouterState state) =>
+            const HomeScreen(),
+      ),
+      GoRoute(
+        path: '/login',
+        builder: (BuildContext context, GoRouterState state) =>
+            const LoginScreen(),
+      ),
+    ],
+
+    // redirect to the login page if the user is not logged in
+    redirect: (BuildContext context, GoRouterState state) {
+      // if the user is not logged in, they need to login
+      final bool loggedIn = _loginInfo.loggedIn;
+      final bool loggingIn = state.matchedLocation == '/login';
+      if (!loggedIn) {
+        return '/login';
+      }
+
+      // if the user is logged in but still on the login page, send them to
+      // the home page
+      if (loggingIn) {
+        return '/';
+      }
+
+      // no need to redirect at all
+      return null;
+    },
+
+    // changes on the listenable will cause the router to refresh it's route
+    refreshListenable: _loginInfo,
+  );
+}
+
+/// The login screen.
+class LoginScreen extends StatelessWidget {
+  /// Creates a [LoginScreen].
+  const LoginScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) => Scaffold(
+        appBar: AppBar(title: const Text(App.title)),
+        body: Center(
+          child: ElevatedButton(
+            onPressed: () {
+              // log a user in, letting all the listeners know
+              context.read<LoginInfo>().login('test-user');
+
+              // router will automatically redirect from /login to / using
+              // refreshListenable
+            },
+            child: const Text('Login'),
+          ),
+        ),
+      );
+}
+
+/// The home screen.
+class HomeScreen extends StatelessWidget {
+  /// Creates a [HomeScreen].
+  const HomeScreen({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    final LoginInfo info = context.read<LoginInfo>();
+
+    return Scaffold(
+      appBar: AppBar(
+        title: const Text(App.title),
+        actions: <Widget>[
+          IconButton(
+            onPressed: info.logout,
+            tooltip: 'Logout: ${info.userName}',
+            icon: const Icon(Icons.logout),
+          )
+        ],
+      ),
+      body: const Center(
+        child: Text('HomeScreen'),
+      ),
+    );
+  }
+}