go_router #

The goal of the go_router package is to simplify use of the Router in Flutter as specified by the MaterialApp.router constructor. By default, it requires an implementation of the RouterDelegate and RouteInformationParser classes. These two implementations themselves imply the definition of a third type to hold the app state that drives the creation of the Navigator. You can read an excellent blog post on these requirements on Medium. This separation of responsibilities allows the Flutter developer to implement a number of routing and navigation policies, including deep and dynamic linking, but at the cost of complexity.

The purpose of the go_router is to use declarative routes to reduce complexity, regardless of the platform you're targeting (mobile, web, desktop), handling deep and dynamic linking from Android, iOS and the web, along with a number of other navigation-related scenarios, while still (hopefully) providing an easy-to-use developer experience.

Table of Contents #

Contributors
Changelog
Migrating to 2.x
Getting Started
Declarative Routing
- Router state
- Error handling
- Initialization
Navigation
- Current location
Initial Location
Parameters
- Dynamic linking
Sub-routes
Pushing pages
Redirection
- Top-level redirection
- Route-level redirection
- Parameterized redirection
- Multiple redirections
Query Parameters
Extra Parameter
Named Routes
- Navigating to Named Routes
- Redirecting to Named Routes
Custom Transitions
Async Data
Nested Navigation
- Keeping State
Navigator Builder
Deep Linking
URL Path Strategy
Debugging Your Routes
Navigator Integration
Examples
Issues

Contributors #

It's amazing to me how many folks have already contributed to this project. Huge shout out to the go_router contributors!

Salakar for the CI action on GitHub that is always helping me track down stuff I forget
rydmike for a bunch of README and dartdoc fixes as well as a great example for keeping state during nested navigation
Abhishek01039 for helping me change a life-long habit of sorting constructors after fields, which goes against Dart best practices
SunlightBro for the Android system Back button fix
craiglabenz for a bunch of README fixes; also, Craig has been talking about adding build_runner support to produce typesafe go and push code for named routes, so thumbs up on this issues if that's a feature you'd like to see in go_router
kevmoo for helping me track down spelling issues in my README and unused imports and refactoring for easier maintenance
andyduke for the most excellent navigationBuilder feature and updates to state restoration.

Changelog #

If you'd like to see what's changed in detail over time, you can read the go_router Changelog.

Migrating to 2.x #

By popular demand, there is a breaking change in the go_router 2.0 release: the params property of the GoRouterState object has been split into two properties:

params for parameters that are part of the path and, e.g. /family/:fid
queryParams for parameters that added optionally at the end of the location, e.g. /login?from=/family/f2

In the 1.x releases, the params property was a single object that contained both the path and query parameters in a single map. For example, if you had been using the params property to access query parameters like this in 1.x:

GoRoute(
  path: '/login',
  pageBuilder: (context, state) => MaterialPage<void>(
    key: state.pageKey,
    // 1.x: accessing query parameters
    child: LoginPage(from: state.params['from']),
  ),
),

in 2.0, you would access the query parameters like this:

GoRoute(
  path: '/login',
  pageBuilder: (context, state) => MaterialPage<void>(
    key: state.pageKey,
    // 2.0: accessing query parameters
    child: LoginPage(from: state.queryParams['from']),
  ),
),

Likewise, if you were using named routes in 1.x, you may have been passing both path and query parameters like so:

ListTile(
  title: Text(p.name),
  // 1.x: passing both path and query parameters
  onTap: () => context.goNamed(
    'person',
    // "extra" path params were query params
    {'fid': family.id, 'pid': p.id, 'qid': 'quid'},
  ),
),

Now you'll need to change your code to do the following in 2.0:

ListTile(
  title: Text(p.name),
  // 2.0: passing both path and query parameters
  onTap: () => context.goNamed(
    'person',
    params: {'fid': family.id, 'pid': p.id},
    queryParams: {'qid': 'quid'},
  ),
),

I got a little clever merging the two kinds of parameters into a single scope and hopefully this change makes things a little more clear.

Getting Started #

To use the go_router package, follow these instructions.

Declarative Routing #

The go_router is governed by a set of routes which you specify as part of the GoRouter constructor:

class App extends StatelessWidget {
  ...
  final _router = GoRouter(
    routes: [
      GoRoute(
        path: '/',
        pageBuilder: (context, state) => MaterialPage<void>(
          key: state.pageKey,
          child: const Page1Page(),
        ),
      ),
      GoRoute(
        path: '/page2',
        pageBuilder: (context, state) => MaterialPage<void>(
          key: state.pageKey,
          child: const Page2Page(),
        ),
      ),
    ],
  ...
  );
}

In this case, we've defined two routes. Each route path will be matched against the location to which the user is navigating. Only a single path will be matched, specifically the one that matches the entire location (and so it doesn't matter in which order you list your routes). The path will be matched in a case-insensitive way, although the case for parameters will be preserved.

Router state #

A GoRoute also contains a pageBuilder function which is called to create the page when a path is matched. The builder function is passed a state object, which is an instance of the GoRouterState class that contains some useful information:

`GoRouterState` property	description	example 1	example 2
`location`	location of the full route, including query params	`/login?from=/family/f2`	`/family/f2/person/p1`
`subloc`	location of this sub-route w/o query params	`/login`	`/family/f2`
`name`	the `GoRoute` name	`login`	`family`
`path`	the `GoRoute` path	`/login`	`family/:fid`
`fullpath`	full path to this sub-route	`/login`	`/family/:fid`
`params`	params extracted from the location	`{}`	`{'fid': 'f2'}`
`queryParams`	optional params from the end of the location	`{'from': '/family/f1'}`	`{}`
`extra`	optional object param	`null`	`null`
`error`	`Exception` associated with this sub-route, if any	`Exception('404')`	...
`pageKey`	unique key for this sub-route	`ValueKey('/login')`	`ValueKey('/family/:fid')`

You can read more about sub-locations/sub-routes and parameterized routes below but the example code above uses the pageKey property as most of the example code does. The pageKey is used to create a unique key for the MaterialPage or CupertinoPage based on the current path for that page in the stack of pages, so it will uniquely identify the page w/o having to hardcode a key or come up with one yourself.

Error handling #

In addition to the list of routes, the go_router needs an errorPageBuilder function in case no page is found, more than one page is found or if any of the page builder functions throws an exception, e.g.

class App extends StatelessWidget {
  ...
  final _router = GoRouter(
    ...
    errorPageBuilder: (context, state) => MaterialPage<void>(
      key: state.pageKey,
      child: ErrorPage(state.error),
    ),
  );
}

The GoRouterState object contains the location that caused the exception and the Exception that was thrown attempting to navigate to that route.

Initialization #

With just a list of routes and an error page builder function, you can create an instance of a GoRouter, which itself provides the objects you need to call the MaterialApp.router constructor:

class App extends StatelessWidget {
  App({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) => MaterialApp.router(
        routeInformationParser: _router.routeInformationParser,
        routerDelegate: _router.routerDelegate,
      );

  final _router = GoRouter(routes: ..., errorPageBuilder: ...);
}

With the router in place, your app can now navigate between pages.

Navigation #

To navigate between pages, use the GoRouter.go method:

// navigate using the GoRouter
onTap: () => GoRouter.of(context).go('/page2')

The go_router also provides a simplified means of navigation using Dart extension methods:

// more easily navigate using the GoRouter
onTap: () => context.go('/page2')

The simplified version maps directly to the more fully-specified version, so you can use either. If you're curious, the ability to just call context.go(...) and have magic happen is where the name of the go_router came from.

If you'd like to navigate via the Link widget, that works, too:

Link(
  uri: Uri.parse('/page2'),
  builder: (context, followLink) => TextButton(
    onPressed: followLink,
    child: const Text('Go to page 2'),
  ),
),

If the Link widget is given a URL with a scheme, e.g. https://flutter.dev, then it will launch the link in a browser. Otherwise, it'll navigate to the link inside the app using the built-in navigation system.

You can also navigate to a named route, discussed below.

Current location #

If you want to know the current location, use the GoRouter.location property. If you'd like to know when the current location changes, either because of manual navigation or a deep link or a pop due to the user pushing the Back button, the GoRouter is a ChangeNotifier, which means that you can call addListener to be notified when the location changes, either manually or via Flutter's builder widget for ChangeNotifier objects, the non-intuitively named AnimatedBuilder:

class RouterLocationView extends StatelessWidget {
  const RouterLocationView({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    final router = GoRouter.of(context);
    return AnimatedBuilder(
      animation: router,
      builder: (context, child) => Text(router.location),
    );
  }
}

Or, if you're using the provider package, it comes with built-in support for re-building a Widget when a ChangeNotifier changes with a type that is much more clearly suited for the purpose.

Initial Location #

If you'd like to set an initial location for routing, you can set the initialLocation argument of the GoRouter constructor:

final _router = GoRouter(
  routes: ...,
  errorPageBuilder: ...,
  initialLocation: '/page2',
);

The value you provide to initialLocation will be ignored if your app is started using deep linking.

Parameters #

The route paths are defined and implemented in the path_to_regexp package, which gives you the ability to include parameters in your route's path:

final _router = GoRouter(
  routes: [
    GoRoute(
      path: '/family/:fid',
      pageBuilder: (context, state) {
        // use state.params to get router parameter values
        final family = Families.family(state.params['fid']!);

        return MaterialPage<void>(
          key: state.pageKey,
          child: FamilyPage(family: family),
        );
      },
    ),
  ],
  errorPageBuilder: ...,
]);

You can access the matched parameters in the state object using the params property.

Dynamic linking #

The idea of "dynamic linking" is that as the user adds objects to your app, each of them gets a link of their own, e.g. a new family gets a new link. This is exactly what route parameters enables, e.g. a new family has its own identifier when can be a variable in your family route, e.g. path: /family/:fid.

Sub-routes #

Every top-level route will create a navigation stack of one page. To produce an entire stack of pages, you can use sub-routes. In the case that a top-level route only matches part of the location, the rest of the location can be matched against sub-routes. The rules are still the same, i.e. that only a single route at any level will be matched and the entire location much be matched.

For example, the location /family/f1/person/p2, can be made to match multiple sub-routes to create a stack of pages:

/             => HomePage()
  family/f1   => FamilyPage('f1')
    person/p2 => PersonPage('f1', 'p2') ← showing this page, Back pops the stack ↑

To specify a set of pages like this, you can use sub-page routing via the routes parameter to the GoRoute constructor:

final _router = GoRouter(
  routes: [
    GoRoute(
      path: '/',
      pageBuilder: (context, state) => MaterialPage<void>(
        key: state.pageKey,
        child: HomePage(families: Families.data),
      ),
      routes: [
        GoRoute(
          path: 'family/:fid',
          pageBuilder: (context, state) {
            final family = Families.family(state.params['fid']!);

            return MaterialPage<void>(
              key: state.pageKey,
              child: FamilyPage(family: family),
            );
          },
          routes: [
            GoRoute(
              path: 'person/:pid',
              pageBuilder: (context, state) {
                final family = Families.family(state.params['fid']!);
                final person = family.person(state.params['pid']!);

                return MaterialPage<void>(
                  key: state.pageKey,
                  child: PersonPage(family: family, person: person),
                );
              },
            ),
          ],
        ),
      ],
    ),
  ],
  errorPageBuilder: ...
);

The go_router will match the routes all the way down the tree of sub-routes to build up a stack of pages. If go_router doesn't find a match, then the error handler will be called.

Also, the go_router will pass parameters from higher level sub-routes so that they can be used in lower level routes, e.g. fid is matched as part of the family/:fid route, but it's passed along to the person/:pid route because it's a sub-route of the family/:fid route.

Pushing pages #

In addition to the go method, the go_router also provides a push method. Both go and push can be used to build up a stack of pages, but in different ways. The go method does this by turning a single location into any number of pages in a stack using Sub-routes.

The push method is used to push a single page onto the stack of existing pages, which means that you can build up the stack programmatically instead of declaratively. When the push method matches an entire stack via sub-routes, it will take the top-most page from the stack and push that page onto the stack.

You can also push a named route, discussed below.

Redirection #

Sometimes you want your app to redirect to a different location. The go_router allows you to do this at a top level for each new navigation event or at the route level for a specific route.

Top-level redirection #

Sometimes you want to guard pages from being accessed when they shouldn't be, e.g. when the user is not yet logged in. For example, assume you have a class that tracks the user's login info:

class LoginInfo extends ChangeNotifier {
  var _userName = '';
  String get userName => _userName;
  bool get loggedIn => _userName.isNotEmpty;

  void login(String userName) {
    _userName = userName;
    notifyListeners();
  }

  void logout() {
    _userName = '';
    notifyListeners();
  }
}

You can use this info in the implementation of a redirect function that you pass as to the GoRouter constructor:

class App extends StatelessWidget {
  final loginInfo = LoginInfo();
  ...
  late final _router = GoRouter(
    routes: [
      GoRoute(
        path: '/',
        pageBuilder: (context, state) => MaterialPage<void>(
          key: state.pageKey,
          child: HomePage(families: Families.data),
        ),
      ),
      ...,
      GoRoute(
        path: '/login',
        pageBuilder: (context, state) => MaterialPage<void>(
          key: state.pageKey,
          child: const LoginPage(),
        ),
      ),
    ],

    errorPageBuilder: ...,

    // redirect to the login page if the user is not logged in
    redirect: (state) {
      final loggedIn = loginInfo.loggedIn;
      final goingToLogin = state.location == '/login';

      // the user is not logged in and not headed to /login, they need to login
      if (!loggedIn && !goingToLogin) return '/login';

      // the user is logged in and headed to /login, no need to login again
      if (loggedIn && goingToLogin) return '/';

      // no need to redirect at all
      return null;
    },
  );
}

In this code, if the user is not logged in and not going to the /login path, we redirect to /login. Likewise, if the user is logged in but going to /login, we redirect to /. If there is no redirect, then we just return null. The redirect function will be called again until null is returned to enable multiple redirects.

To make it easy to access this info wherever it's need in the app, consider using a state management option like provider to put the login info into the widget tree:

class App extends StatelessWidget {
  final loginInfo = LoginInfo();

  // 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(...),
      );
  ...
}

With the login info in the widget tree, you can easily implement your login page:

class LoginPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) => Scaffold(
    appBar: AppBar(title: Text(_title(context))),
    body: Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: () {
              // log a user in, letting all the listeners know
              context.read<LoginInfo>().login('test-user');

              // go home
              context.go('/');
            },
            child: const Text('Login'),
          ),
        ],
      ),
    ),
  );
}

In this case, we've logged the user in and manually redirected them to the home page. That's because the go_router doesn't know that the app's state has changed in a way that affects the route. If you'd like to have the app's state cause go_router to automatically redirect, you can use the refreshListenable argument of the GoRouter constructor:

class App extends StatelessWidget {
  final loginInfo = LoginInfo();
  ...
  late final _router = GoRouter(
    routes: ...,
    errorPageBuilder: ...,
    redirect: ...

    // changes on the listenable will cause the router to refresh it's route
    refreshListenable: loginInfo,
  );
}

Since the loginInfo is a ChangeNotifier, it will notify listeners when it changes. By passing it to the GoRouter constructor, the go_router will automatically refresh the route when the login info changes. This allows you to simplify the login logic in your app:

onPressed: () {
  // log a user in, letting all the listeners know
  context.read<LoginInfo>().login('test-user');

  // router will automatically redirect from /login to / because login info
  //context.go('/');
},

The use of the top-level redirect and refreshListenable together is recommended because it will handle the routing automatically for you when the app's data changes.

Route-level redirection #

The top-level redirect handler passed to the GoRouter constructor is handy when you want a single function to be called whenever there's a new navigation event and to make some decisions based on the app's current state. However, in the case that you'd like to make a redirection decision for a specific route (or sub-route), you can do so by passing a redirect function to the GoRoute constructor:

final _router = GoRouter(
  routes: [
    GoRoute(
      path: '/',
      redirect: (_) => '/family/${Families.data[0].id}',
    ),
    GoRoute(
      path: '/family/:fid',
      pageBuilder: ...,
  ],
  errorPageBuilder: ...,
);

In this case, when the user navigates to /, the redirect function will be called to redirect to the first family's page. Redirection will only occur on the last sub-route matched, so you can't have to worry about redirecting in the middle of a location being parsed when you're already on your way to another page anyway.

Parameterized redirection #

In some cases, a path is parameterized, and you'd like to redirect with those parameters in mind. You can do that with the params argument to the state object passed to the redirect function:

GoRoute(
  path: '/author/:authorId',
  redirect: (state) => '/authors/${state.params['authorId']}',
),

Multiple redirections #

It's possible to redirect multiple times w/ a single navigation, e.g. / => /foo => /bar. This is handy because it allows you to build up a list of routes over time and not to worry so much about attempting to trim each of them to their direct route. Furthermore, it's possible to redirect at the top level and at the route level in any number of combinations.

If you redirect too many times, that's likely to indicate a bug in your app. By default, more than 5 redirections will cause an exception. You can change this by setting the redirectLimit argument to the GoRouter constructor.

The other trouble you need worry about is getting into a loop, e.g. / => /foo => /. If that happens, you'll get an exception.

Query Parameters #

Sometimes you're doing deep linking and you'd like a user to first login before going to the location that represents the deep link. In that case, you can use query parameters in the redirect function:

class App extends StatelessWidget {
  final loginInfo = LoginInfo();
  ...
  late final _router = GoRouter(
    routes: ...,
    errorPageBuilder: ...,

    // redirect to the login page if the user is not logged in
    redirect: (state) {
      final loggedIn = loginInfo.loggedIn;

      // check just the subloc in case there are query parameters
      final goingToLogin = state.subloc == '/login';

      // the user is not logged in and not headed to /login, they need to login
      if (!loggedIn && !goingToLogin) return '/login?from=${state.subloc}';

      // the user is logged in and headed to /login, no need to login again
      if (loggedIn && goingToLogin) return '/';

      // no need to redirect at all
      return null;
    },

    // changes on the listenable will cause the router to refresh it's route
    refreshListenable: loginInfo,
  );
}

In this example, if the user isn't logged in, they're redirected to /login with a from query parameter set to the deep link. The state object has the location and the subloc to choose from. The location includes the query parameters whereas the subloc does not. Since the /login route may include query parameters, it's easiest to use the subloc in this case (and using the raw location will cause a stack overflow, an exercise that I'll leave to the reader).

Now, when the /login route is matched, we want to pull the from parameter out of the state object to pass along to the LoginPage:

GoRoute(
  path: '/login',
  pageBuilder: (context, state) => MaterialPage<void>(
    key: state.pageKey,
    // pass the original location to the LoginPage (if there is one)
    child: LoginPage(from: state.queryParams['from']),
  ),
),

In the LoginPage, if the from parameter was passed, we use it to go to the deep link location after a successful login:

class LoginPage extends StatelessWidget {
  final String? from;
  const LoginPage({this.from, Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) => Scaffold(
    appBar: AppBar(title: Text(_title(context))),
    body: Center(
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: () {
              // log a user in, letting all the listeners know
              context.read<LoginInfo>().login('test-user');

              // if there's a deep link, go there
              if (from != null) context.go(from!);
            },
            child: const Text('Login'),
          ),
        ],
      ),
    ),
  );
}

It's still good practice to pass in the refreshListenable when manually redirecting, as we do in this case, to ensure any change to the login info causes the right routing to happen automatically, e.g. the user logging out will cause them to be routed back to the login page.

Extra parameter #

In addition to passing along path and query parameters, you can also pass along an extra object as part of your navigation, e.g.

void _tap(BuildContext context, Family family) =>
  context.go('/family', extra: family);

This object is available during the pageBuilder function as state.extra:

GoRoute(
  path: '/family',
  pageBuilder: (context, state) => MaterialPage<Family>(
    key: state.pageKey,
    child: FamilyPage(family: state.extra! as Family),
  ),
),

The extra object is useful if you'd like to simply pass along a single object to the pageBuilder function w/o passing an object identifier via a URI and looking up the object from a store. However, this object cannot be used to create a dynamic link, cannot be used in deep linking and so is not recommended for those cases.

Named Routes #

When you're navigating to a route with a location, you're hardcoding the URI construction into your app, e.g.

void _tap(BuildContext context, String fid, String pid) =>
  context.go('/family/$fid/person/$pid');

Not only is that error-prone, but the actual URI format of your app could change over time. Certainly redirection helps keep old URI formats working, but do you really want various versions of your location URIs lying around willy-nilly in your code?

Navigating to Named Routes #

The idea of named routes is to make it easy to navigate to a route w/o knowing or caring what the URI format is. You can add a unique name to your route using the GoRoute.name parameter:

final _router = GoRouter(
  routes: [
    GoRoute(
      name: 'home',
      path: '/',
      pageBuilder: ...,
      routes: [
        GoRoute(
          name: 'family',
          path: 'family/:fid',
          pageBuilder: ...,
          routes: [
            GoRoute(
              name: 'person',
              path: 'person/:pid',
              pageBuilder: ...,
            ),
          ],
        ),
      ],
    ),
    GoRoute(
      name: 'login',
      path: '/login',
      pageBuilder: ...,
    ),
  ],

You don't need to name any of your routes but the ones that you do name, you can navigate to using the name and whatever params are needed:

void _tap(BuildContext context, String fid, String pid) =>
  context.go(context.namedLocation('person', params: {'fid': fid, 'pid': pid}));

The namedLocation method will look up the route by name in a case-insensitive way, construct the URI for you and fill in the params as appropriate. If you miss a param or pass in params that aren't part of the path, you'll get an error. Since it's somewhat inconvenient to have to dereference the context object twice, go_router provides a goNamed method that does the lookup and navigation in one step:

void _tap(BuildContext context, String fid, String pid) =>
  context.goNamed('person', params: {'fid': fid, 'pid': pid});

There is also a pushNamed method that will look up the route by name, pull the top page off of the generated match stack and push that onto the existing stack of pages.

Redirecting to Named Routes #

In addition to navigation, you may also want to be able to redirect to a named route, which you can also do using the namedLocation method of either GoRouter or GoRouterState:

// redirect to the login page if the user is not logged in
redirect: (state) {
  final loggedIn = loginInfo.loggedIn;

  // check just the subloc in case there are query parameters
  final loginLoc = state.namedLocation('login');
  final goingToLogin = state.subloc == loginLoc;

  // the user is not logged in and not headed to /login, they need to login
  if (!loggedIn && !goingToLogin)
    return state.namedLocation('login', queryParams: {'from': state.subloc});

  // the user is logged in and headed to /login, no need to login again
  if (loggedIn && goingToLogin) return state.namedLocation('home');

  // no need to redirect at all
  return null;
},

In this example, we're using namedLocation to get the location for the named 'login' route and then comparing it to the current subloc to find out if the user is currently logging in or not. Furthermore, when we construct a location for redirection, we use namedLocation to pass in parameters to construct the location. All of this is done without hardcoding any URI formatting into your code.

Custom Transitions #

As you transition between routes, you get transitions based on whether you're using MaterialPage or CupertinoPage; each of them implements the transitions as defined by the underlying platform. However, if you'd like to implement a custom transition, you can do so by using the CustomTransitionPage provided with go_router:

GoRoute(
  path: '/fade',
  pageBuilder: (context, state) => CustomTransitionPage<void>(
    key: state.pageKey,
    child: const TransitionsPage(kind: 'fade', color: Colors.red),
    transitionsBuilder: (context, animation, secondaryAnimation, child) =>
        FadeTransition(opacity: animation, child: child),
  ),
),

The transitionBuilder argument to the CustomTransitionPage is called when you're routing to a new route, and it's your chance to return a transition widget. The transitions sample shows off four different kind of transitions, but really you can do whatever you want.

custom transitions example

The CustomTransitionPage constructor also takes a transitionsDuration argument in case you'd like to customize the duration of the transition as well (it defaults to 300ms).

Async Data #

Sometimes you'll want to load data asynchronously, and you'll need to wait for the data before showing content. Flutter provides a way to do this with the FutureBuilder widget that works just the same with the go_router as it always does in Flutter. For example, imagine you've got a Repository class that does network communication when it looks up data:

class Repository {
  Future<List<Family>> getFamilies() async { /* network comm */ }
  Future<Family> getFamily(String fid) async => { /* network comm */ }
  ...
}

Now you can use the FutureBuilder to show a loading indicator while the data is loading:

class App extends StatelessWidget {
  final repo = Repository();
  ...
  late final _router = GoRouter(
    routes: [
      GoRoute(
        path: '/',
        pageBuilder: (context, state) => NoTransitionPage<void>(
          key: state.pageKey,
          child: FutureBuilder<List<Family>>(
            future: repo.getFamilies(),
            pageBuilder: (context, snapshot) {
              if (snapshot.hasError)
                return ErrorPage(snapshot.error as Exception?);
              if (snapshot.hasData) return HomePage(families: snapshot.data!);
              return const Center(child: CircularProgressIndicator());
            },
          ),
        ),
        routes: [
          GoRoute(
            path: 'family/:fid',
            pageBuilder: (context, state) => NoTransitionPage<void>(
              key: state.pageKey,
              child: FutureBuilder<Family>(
                future: repo.getFamily(state.params['fid']!),
                pageBuilder: (context, snapshot) {
                  if (snapshot.hasError)
                    return ErrorPage(snapshot.error as Exception?);
                  if (snapshot.hasData)
                    return FamilyPage(family: snapshot.data!);
                  return const Center(child: CircularProgressIndicator());
                },
              ),
            ),
            routes: [
              GoRoute(
                path: 'person/:pid',
                pageBuilder: (context, state) => NoTransitionPage<void>(
                  key: state.pageKey,
                  child: FutureBuilder<FamilyPerson>(
                    future: repo.getPerson(
                      state.params['fid']!,
                      state.params['pid']!,
                    ),
                    pageBuilder: (context, snapshot) {
                      if (snapshot.hasError)
                        return ErrorPage(snapshot.error as Exception?);
                      if (snapshot.hasData)
                        return PersonPage(
                            family: snapshot.data!.family,
                            person: snapshot.data!.person);
                      return const Center(child: CircularProgressIndicator());
                    },
                  ),
                ),
              ),
            ],
          ),
        ],
      ),
    ],
    errorPageBuilder: (context, state) => MaterialPage<void>(
      key: state.pageKey,
      child: ErrorPage(state.error),
    ),
  );
}

class NoTransitionPage<T> extends CustomTransitionPage<T> {
  const NoTransitionPage({required Widget child, LocalKey? key})
      : super(transitionsBuilder: _transitionsBuilder, child: child, key: key);

  static Widget _transitionsBuilder(
          BuildContext context,
          Animation<double> animation,
          Animation<double> secondaryAnimation,
          Widget child) =>
      child;
}

This is a simple case that shows a circular progress indicator while the data is being loaded and before the page is shown.

async data example

The way transitions work, the outgoing page is shown for a little while before the incoming page is shown, which looks pretty terrible when your page is doing nothing but showing a circular progress indicator. I admit that I took the coward's way out and turned off the transitions so that things wouldn't look so bad in the animated screenshot. However, it would be nicer to keep the transition, navigate to the page showing as much as possible, e.g. the AppBar, and then show the loading indicator inside the page itself. In that case, you'll be on your own to show an error in the case that the data can't be loaded. Such polish is left as an exercise for the reader.

Nested Navigation #

Sometimes you want to choose a page based on a route as well as the state of that page, e.g. the currently selected tab. In that case, you want to choose not just the page from a route but also the widgets nested inside the page. That's called "nested navigation". The key differentiator for "nested" navigation is that there's no transition on the part of the page that stays the same, e.g. the app bar stays the same as you navigate to different tabs on this TabView:

Of course, you can easily do this using the TabView widget, but what makes this nested "navigation" is that the location of the page changes, i.e. notice the address bar as the user transitions from tab to tab. This makes it easy for the user to capture a dynamic link for any object in the app, enabling deep linking.

To use nested navigation using go_router, you can simply navigate to the same page via different paths or to the same path with different parameters, with the differences dictating the different state of the page. For example, to implement that page with the TabView above, you need a widget that changes the selected tab via a parameter:

class FamilyTabsPage extends StatefulWidget {
  final int index;
  FamilyTabsPage({required Family currentFamily, Key? key})
      : index = Families.data.indexWhere((f) => f.id == currentFamily.id),
        super(key: key) {
    assert(index != -1);
  }

  @override
  _FamilyTabsPageState createState() => _FamilyTabsPageState();
}

class _FamilyTabsPageState extends State<FamilyTabsPage>
    with TickerProviderStateMixin {
  late final TabController _controller;

  @override
  void initState() {
    super.initState();
    _controller = TabController(
      length: Families.data.length,
      vsync: this,
      initialIndex: widget.index,
    );
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();
    _controller.index = widget.index;
  }

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: Text(_title(context)),
          bottom: TabBar(
            controller: _controller,
            tabs: [for (final f in Families.data) Tab(text: f.name)],
            onTap: (index) => _tap(context, index),
          ),
        ),
        body: TabBarView(
          controller: _controller,
          children: [for (final f in Families.data) FamilyView(family: f)],
        ),
      );

  void _tap(BuildContext context, int index) =>
      context.go('/family/${Families.data[index].id}');

  String _title(BuildContext context) =>
      (context as Element).findAncestorWidgetOfExactType<MaterialApp>()!.title;
}

The FamilyTabsPage is a stateful widget that takes the currently selected family as a parameter. It uses the index of that family in the list of families to set the currently selected tab. However, instead of switching the currently selected tab to whatever the user clicks on, it uses navigation to get to that index instead. It's the use of navigation that changes the address in the address bar. And, the way that the tab index is switched is via the call to didChangeDependencies. Because the FamilyTabsPage is a stateful widget, the widget itself can be changed but the state is kept. When that happens, the call to didChangeDependencies will change the index of the TabController to match the new navigation location.

To implement the navigation part of this example, we need a route that translates the location into an instance of FamilyTabsPage parameterized with the currently selected family:

final _router = GoRouter(
  routes: [
    GoRoute(
      path: '/',
      redirect: (_) => '/family/${Families.data[0].id}',
    ),
    GoRoute(
      path: '/family/:fid',
      pageBuilder: (context, state) {
        final fid = state.params['fid']!;
        final family = Families.data.firstWhere((f) => f.id == fid,
            orElse: () => throw Exception('family not found: $fid'));

        return MaterialPage<void>(
          key: state.pageKey,
          child: FamilyTabsPage(key: state.pageKey, currentFamily: family),
        );
      },
    ),
  ],
  
  errorPageBuilder: ...,
);

The / route is a redirect to the first family. The /family/:fid route is the one that sets up nested navigation. It does this by first creating an instance of FamilyTabsPage with the family that matches the fid parameter. And second, it uses state.pageKey to signal to Flutter that this is the same page as before. This combination is what causes the router to leave the page alone, to update the browser's address bar and to let the TabView navigate to the new selection.

This may seem like a lot, but in summary, you need to do three things with the page you create in your page builder to support nested navigation:

Use a StatefulWidget as the base class of the thing you pass to MaterialPage (or whatever).
Pass the same key value to the MaterialPage so that Flutter knows that you're keeping the same state for your StatefulWidget-derived page; state.pageKey is handy for this.
As the user navigates, you'll create the same StatefulWidget-derived type, passing in new data, e.g. which tab is currently selected. Because you're using a widget with the same key, Flutter will keep the state but swap out the widget wrapping w/ the new data as constructor args. When that new widget wrapper is in place, Flutter will call didChangeDependencies so that you can use the new data to update the existing widgets, e.g. the selected tab.

This example shows off the selected tab on a TabView but you can use it for any nested content of a page your app navigates to.

Keeping State #

When doing nested navigation, the user expects that widgets will be in the same state that they left them in when they navigated to a new page and return, e.g. scroll position, text input values, etc. You can enable support for this by using AutomaticKeepAliveClientMixin on a stateful widget. You can see this in action in the FamiliyView of the nested_nav.dart example:

class FamilyView extends StatefulWidget {
  const FamilyView({required this.family, Key? key}) : super(key: key);
  final Family family;

  @override
  State<FamilyView> createState() => _FamilyViewState();
}

/// Use the [AutomaticKeepAliveClientMixin] to keep the state.
class _FamilyViewState extends State<FamilyView>
    with AutomaticKeepAliveClientMixin {
      
  // Override `wantKeepAlive` when using `AutomaticKeepAliveClientMixin`.
  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    // Call `super.build` when using `AutomaticKeepAliveClientMixin`.
    super.build(context);
    return ListView(
      children: [
        for (final p in widget.family.people)
          ListTile(
            title: Text(p.name),
            onTap: () =>
                context.go('/family/${widget.family.id}/person/${p.id}'),
          ),
      ],
    );
  }
}

To instruct the AutomaticKeepAliveClientMixin to keep the state, you need to override wantKeepAlive to return true and call super.build in the State class's build method, as show above.

keeping state example

Notice that after scrolling to the bottom of the long list of children in the Hunting family, then going to another tab and then going to another page, when you return to the list of Huntings that the scroll position is maintained.

Navigator Builder #

Sometimes it is necessary to insert a widget above the Navigator, but below MaterialApp/CupertinoApp, e.g. to insert a provider that needs access to the app's context to get the current locale and localization, to build a UI outside of navigation or to completely replace with Navigator with something of your own (which is outside the scope of this document).

For these purposes, you need to use the navigatorBuilder parameter in the GoRouter constructor. This is similar to the builder parameter in the MaterialApp constructor, but gives access to infrastructure provided by MaterialApp.

An example of placing some data provider widget:

final _router = GoRouter(
  routes: ...,
  errorPageBuilder: ...,
  redirect: ...,
  refreshListenable: ...,

  // add a wrapper around the navigator to put loginInfo into the widget tree
  navigatorBuilder: (context, child) =>
      ChangeNotifierProvider<LoginInfo>.value(
    value: loginInfo,
    child: child,
    builder: (context, child) => child!,
  ),
);

A more interesting example of using navigatorBuilder is the following, which puts a floating button on every page to allow for easy logout:

final _router = GoRouter(
  routes: ...,
  errorPageBuilder: ...,
  redirect: ...,
  refreshListenable: ...,

  // add a wrapper around the navigator to:
  // - put loginInfo into the widget tree, and to
  // - add an overlay to show a logout option
  navigatorBuilder: (context, child) =>
      ChangeNotifierProvider<LoginInfo>.value(
    value: loginInfo,
    child: child,
    builder: (context, child) => loginInfo.loggedIn
        ? AuthOverlay(onLogout: loginInfo.logout, child: child!)
        : child!,
  ),
);

This example checks the login status in the navigatorBuilder:

if the user is logged in, an instance of the AuthOverlay widget is created, which wraps the the Navigator passed to navigationBuilder via the child parameter and provides a logout button on every page
if the user is not logged in, return the Navigator via the child parameter

The AuthOverlay shows the logout button and the Navigator in a Stack:

class AuthOverlay extends StatelessWidget {
  const AuthOverlay({
    required this.onLogout,
    required this.child,
    Key? key,
  }) : super(key: key);

  final Widget child;
  final VoidCallback onLogout;

  @override
  Widget build(BuildContext context) => Stack(
        children: [
          child,
          Positioned(
            top: 90,
            right: 4,
            child: ElevatedButton(
              onPressed: onLogout,
              child: const Icon(Icons.logout),
            ),
          ),
        ],
      );
}

Here's what this look like in action:

navigationBuilder in
action

Deep Linking #

Flutter defines "deep linking" as "opening a URL displays that screen in your app." Anything that's listed as a GoRoute can be accessed via deep linking across Android, iOS and the web. Support works out of the box for the web, of course, via the address bar, but requires additional configuration for Android and iOS as described in the Flutter docs.

URL Path Strategy #

By default, Flutter adds a hash (#) into the URL for web apps:

URL Strategy w/ Hash

The process for turning off the hash is documented but fiddly. The go_router has built-in support for setting the URL path strategy, however, so you can simply call GoRouter.setUrlPathStrategy before calling runApp and make your choice:

void main() {
  // turn on the # in the URLs on the web (default)
  // GoRouter.setUrlPathStrategy(UrlPathStrategy.hash);

  // turn off the # in the URLs on the web
  GoRouter.setUrlPathStrategy(UrlPathStrategy.path);

  runApp(App());
}

Setting the path instead of the hash strategy turns off the # in the URLs:

URL Strategy w/o Hash

If your router is created as part of the construction of the widget passed to the runApp method, you can use a shortcut to set the URL path strategy by using the urlPathStrategy parameter of the GoRouter constructor:

 // no need to call GoRouter.setUrlPathStrategy() here
 void main() => runApp(App());

/// sample app using the path URL strategy, i.e. no # in the URL path
class App extends StatelessWidget {
  ...
  final _router = GoRouter(
    routes: ...,
    errorPageBuilder: ...,

    // turn off the # in the URLs on the web
    urlPathStrategy: UrlPathStrategy.path,
  );
}

Finally, when you deploy your Flutter web app to a web server, it needs to be configured such that every URL ends up at your Flutter web app's index.html, otherwise Flutter won't be able to route to your pages. If you're using Firebase hosting, you can configure rewrites to cause all URLs to be rewritten to index.html.

If you'd like to test your release build locally before publishing, and get that cool redirect to index.html feature, you can use flutter run itself:

$ flutter run -d chrome --release lib/url_strategy.dart

Note that you have to run this command from a place where flutter run can find the web/index.html file.

Of course, any local web server that can be configured to redirect all traffic to index.html will do, e.g. live-server.

Debugging Your Routes #

Because go_router asks that you provide a set of paths, sometimes as fragments to match just part of a location, it's hard to know just what routes you have in your app. In those cases, it's handy to be able to see the full paths of the routes you've created as a debugging tool, e.g.

GoRouter: known full paths for routes:
GoRouter:   => /
GoRouter:   =>   /family/:fid
GoRouter:   =>     /family/:fid/person/:pid
GoRouter: known full paths for route names:
GoRouter:   home => /
GoRouter:   family => /family/:fid
GoRouter:   person => /family/:fid/person/:pid

Likewise, there are multiple ways to navigate, e.g. context.go(), context.goNamed(), context.push(), context.pushNamed(), the Link widget, etc., as well as redirection, so it's handy to be able to see how that's going under the covers, e.g.

GoRouter: setting initial location /
GoRouter: location changed to /
GoRouter: getting location for name: "person", params: {fid: f2, pid: p1}
GoRouter: going to /family/f2/person/p1
GoRouter: location changed to /family/f2/person/p1

Finally, if there's an exception in your routing, you'll see that in the debug output, too, e.g.

GoRouter: Exception: no routes for location: /foobarquux

To enable this kind of output when your GoRouter is first created, you can use the debugLogDiagnostics argument:

final _router = GoRouter(
  routes: ...,
  errorPageBuilder: ...,

  // log diagnostic info for your routes
  debugLogDiagnostics: true,
);

This parameter defaults to false, which produces no output.

Navigator Integration #

If you'd like to integrate with the built in Navigator widget, you can, as shown in this snippet from the navigator integration example:

Future<void> _addPerson(BuildContext context) async {
  final person = await Navigator.push<Person>(
    context,
    MaterialPageRoute(
      builder: (context) => NewPersonPage(family: widget.family),
    ),
  );

  if (person != null) {
    setState(() => widget.family.people.add(person));
    context.goNamed('person', params: {
      'fid': widget.family.id,
      'pid': person.id,
    });
  }
}

This example shows how to use the Navigator widget to push a new page and gather the result. It doesn't use the GoRouter but works just the way you'd expect, e.g. it will create a new page on the stack of pages, show a Back button in the AppBar, etc. To return results, use Navigator.pop as you normally would:

ButtonBar(children: [
  TextButton(
    onPressed: () => Navigator.pop(context),
    child: const Text('Cancel'),
  ),
  ElevatedButton(
    onPressed: () {
      if (_formKey.currentState!.validate()) {
        final person = Person(
          id: 'p${widget.family.people.length + 1}',
          name: _nameController.text,
          age: int.parse(_ageController.text),
        );

        Navigator.pop(context, person);
      }
    },
    child: const Text('Create'),
  ),
]),

You can feel free to use GoRouter and Navigator together like this. However, one thing that using Navigator.push in this way will not do is update the browser's address bar. If you want that, you'll need to use GoRouter.go or GoRouter.push. You'll notice, however, that neither go nor push provides for waiting on results. That's because GoRouter is meant for use with deep and dynamic linking, i.e. everything about a location in your app can be expressed as a link. If you're calling Navigator.push and waiting on the results from some random place in your app, that's not something that can be represented in a link.

However, that doesn't mean that you can't use GoRouter to navigate to a page that gathers user input; in fact, I expect that to happen all of the time. Because the results of the navigation are not available to the caller when using the GoRouter, the page itself would be responsible for managing what happens to the user input, e.g.

ButtonBar(children: [
  TextButton(
    onPressed: () =>
      // Navigator.pop(context) would work here, too
      context.goNamed('family', params: {'fid': widget.family.id}),
    child: const Text('Cancel'),
  ),
  ElevatedButton(
    onPressed: () {
      if (_formKey.currentState!.validate()) {
        final person = Person(
          id: 'p${widget.family.people.length + 1}',
          name: _nameController.text,
          age: int.parse(_ageController.text),
        );

        widget.family.people.add(person);

        context.goNamed('person', params: {
          'fid': widget.family.id,
          'pid': person.id,
        });
      }
    },
    child: const Text('Create'),
  ),
]),

With this implementation, you can set up a sub-route to provide a page to add a new person:

GoRoute(
  name: 'home',
  path: '/',
  pageBuilder: ...,
  routes: [
    GoRoute(
      name: 'family',
      path: 'family/:fid',
      pageBuilder: ...,
      routes: [
        GoRoute(
          name: 'person',
          path: 'person/:pid',
          pageBuilder: ...,
        ),
        GoRoute(
          name: 'new-person',
          path: 'new-person',
          pageBuilder: (context, state) {
            final family = Families.family(state.params['fid']!);

            return MaterialPage<void>(
              key: state.pageKey,
              child: NewPersonPage(family: family),
            );
          },
        ),
      ],
    ),
  ],
),

And now your _addPerson method would look like this:

void _addPerson(BuildContext context) {
  context.goNamed('new-person', params: {'fid': widget.family.id});
}

And finally, when you're making changes to the data in your app that appears in more than one place, e.g. updating the list of Person objects in a Family on one page while also showing a list of those Person objects on another page, you'll want to ensure that the widgets in your app can be rebuilt when the state they depend on changes. For this, I recommend a state management solution like provider.

There's no reason not to use the Navigator in your app when you're using the GoRouter, but you'll want to be careful how you manage your app's state and the implications of using Navigator vs. GoRouter for navigation.

Examples #

You can see the go_router in action via the following examples:

main.dart: define a basic routing policy using a set of declarative GoRoute objects
init_loc.dart: start at a specific location instead of home (/), which is the default
sub_routes.dart: provide a stack of pages based on a set of sub routes
push.dart: provide a stack of pages based on a series of calls to context.push()
redirection.dart: redirect one route to another based on changing app state
query_params.dart: optional query parameters will be passed to all page builders
named_routes.dart: navigate via name instead of location URI
transitions.dart: use custom transitions during routing
async_data.dart: async data lookup
nested_nav.dart: include information about children on a page as part of the route path
nav_builder.dart: inject widgets above the Navigator widget
url_strategy.dart: turn off the # in the Flutter web URL
navigator_integration.dart: using Navigator to navigate to a page that gathers user input
state_restoration.dart: test to ensure that go_router works with state restoration (it does)
cupertino.dart: test to ensure that go_router works with the Cupertino design language as well as Material (it does)
books/main.dart: update of the navigation_and_routing sample to use go_router

You can run these examples from the command line like so (from the example folder):

$ flutter run lib/main.dart

Or, if you're using Visual Studio Code, a launch.json file has been provided with these examples configured.

Issues #

Do you have an issue with or feature request for go_router? Log it on the issue tracker.

go_router 2.2.3 go_router: ^2.2.3 copied to clipboard

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