FlowBuilder<FlowState>(
  // The state of the flow.
  state: FlowState(),
  // `VoidCallback` invoked whenever the route location changes.
  // Responsible for reacting to changes in the location.
  //
  // * Will be invoked immediately when the app is launched
  // to determine what the initial state of the flow should be.
  // * Will be invoked when the current route changes via `pushNamed`, `pushReplacementNamed`, etc.
  onLocationChanged: (BuildContext context, FlowLocation location) {
    // Equivalent to `window.location.pathname`.
    final String path = location.path;

    // Map of query parameters which are analagous to `window.location.search`.
    final Map<String, String> params = location.params;

    // Determine the flow state based on the current location.
    final FlowState state = _determineFlowState(path, params);

    /// Update the flow state.
    context.flow<FlowState>().update((_) => state);
  },
  // Called whenever the flow state changes. Will remaing unchanged.
  // Responsible for determining the correct navigation stack
  // based on the current flow state.
  onGeneratePages: (FlowState state, List<Page> currentPages) {
    final List<Page> pages = _determinePages(state, currentPages);
    return pages;
  }
)

const profilePath = 'profile';

...

FlowBuilder<Profile>(
  state: Profile(),
  onLocationChanged: (BuildContext context, FlowLocation location) {
    if (location.path != profilePath) return;
    // Alternatively we can potentially use `fromJson` with `package:json_serializable`.
    // `final profile = Profile.fromJson(location.params);`
    final profile = Profile(
      name: location.params['name'] as String?,
      age: int.tryParse(location.params['age'] as String?)
    );
    context.flow<Profile>().update((_) => profile);
  },
  onGeneratePages: (Profile profile, List<Page> pages) {
    return [
      FlowPage<void>(
        child: ProfileNameForm(),
        location: FlowLocation(path: profilePath),
      ),
      if (profile.name != null)
        FlowPage<void>(
          child: ProfileAgeForm(),
          location: FlowLocation(path: profilePath, params: {'name': profile.name})
        ),
    ]
  }
)

enum AuthState { uninitialized, unauthenticated, authenticated }

class AuthBloc extends Bloc<AuthEvent, AuthState> {...}

FlowBuilder<AuthState>(
  state: context.watch<AuthBloc>().state,
  onGeneratePages: (AuthState state, List<Page> pages) {
    switch (state) {
      case AuthState.uninitialized:
        return [Splash.page()];
      case AuthState.unauthenticated:
        return [Login.page()];
      case AuthState.authenticated:
        return [Home.page()];
    }
  }
)

class Login extends StatelessWidget {

  ...

  @override
  Widget build(BuildContext context) {
    ...
    ElevatedButton(
      onPressed: () => Navigator.of(context).push(SignUp.page());
    )
  }
}

class SignUp extends StatelessWidget {

  ...

  @override
  Widget build(BuildContext context) {
    return FlowBuilder<SignUpState>(
      ...
    )
  }
}