Route Alarms

_{Estimated reading time: 5 minutes}

This example demonstrates how to build a Flutter app using the Maps SDK to calculate and navigate a route containing a speed limit overlay and receive notifications.

How It Works

The example app highlights the following features:

• Calculate a route.
• Simulate navigation on a route.
• Register a listener to receive alarm notifications.

Initial screen	Displaying a screenshot of the computed route

UI and Map Integration

The following code builds the UI with a GemMap widget and an app bar that includes buttons for computing and navigating a route. When the simulated position tracker gets within 500m proximity of the speed limit overlay, an alarm notification is triggered and displayed on the screen.

const projectApiToken = String.fromEnvironment('GEM_TOKEN');
void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Route Alarms',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late GemMapController _mapController;

  bool _areRoutesBuilt = false;
  bool _isSimulationActive = false;

  // We use the progress listener to cancel the route calculation.
  TaskHandler? _routingHandler;

  // We use the progress listener to cancel the navigation.
  TaskHandler? _navigationHandler;
  AlarmService? _alarmService;
  AlarmListener? _alarmListener;

  // The closest alarm and its associated distance and image
  OverlayItemPosition? _closestOverlayItem;

  @override
  void dispose() {
    GemKit.release();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text(
          "Route Alarms",
          style: TextStyle(color: Colors.white),
        ),
        backgroundColor: Colors.deepPurple[900],
        actions: [
          if (!_isSimulationActive && _areRoutesBuilt)
            IconButton(
              onPressed: _startSimulation,
              icon: const Icon(Icons.play_arrow, color: Colors.white),
            ),
          if (_isSimulationActive)
            IconButton(
              onPressed: _stopSimulation,
              icon: const Icon(Icons.stop, color: Colors.white),
            ),
          if (!_areRoutesBuilt)
            IconButton(
              onPressed: () => _onBuildRouteButtonPressed(context),
              icon: const Icon(Icons.route, color: Colors.white),
            ),
        ],
      ),
      body: Stack(
        children: [
          GemMap(
            key: ValueKey("GemMap"),
            onMapCreated: _onMapCreated,
            appAuthorization: projectApiToken,
          ),
          if (_closestOverlayItem != null)
            Positioned(
              bottom: MediaQuery.of(context).padding.bottom + 10,
              left: 0,
              child: BottomAlarmPanel(
                remainingDistance: _closestOverlayItem!.distance.toString(),
                image:
                    _closestOverlayItem!.overlayItem.img.isValid
                        ? _closestOverlayItem!.overlayItem.img
                            .getRenderableImageBytes()
                        : null,
              ),
            ),
        ],
      ),
      resizeToAvoidBottomInset: false,
    );
  }

  void _onMapCreated(GemMapController controller) {
    _mapController = controller;
  }

  // Custom method for calling calculate route and displaying the results.
  void _onBuildRouteButtonPressed(BuildContext context) {
    // Define the departure.
    final departureLandmark = Landmark.withLatLng(
      latitude: 50.92899490001731,
      longitude: 9.544136681645025,
    );

    // Define the destination.
    final destinationLandmark = Landmark.withLatLng(
      latitude: 50.919902402432946,
      longitude: 9.55855522546262,
    );
    // Define the route preferences.
    final routePreferences = RoutePreferences();
    _showSnackBar(context, message: 'The route is calculating.');

    // Calling the calculateRoute SDK method.
    // (err, results) - is a callback function that gets called when the route computing is finished.
    // err is an error enum, results is a list of routes.
    _routingHandler = RoutingService.calculateRoute(
      [departureLandmark, destinationLandmark],
      routePreferences,
      (err, routes) async {
        // If the route calculation is finished, we don't have a progress listener anymore.
        _routingHandler = null;

        ScaffoldMessenger.of(context).clearSnackBars();

        // If there aren't any errors, we display the routes.
        if (err == GemError.success) {
          // Get the routes collection from map preferences.
          final routesMap = _mapController.preferences.routes;

          // Display the routes on map.
          for (final route in routes) {
            routesMap.add(route, route == routes.first);
          }

          // Center the camera on routes.
          _mapController.centerOnRoutes(routes: routes);
        }
        setState(() {
          _areRoutesBuilt = true;
        });
      },
    );
  }

  // Method for starting the simulation and following the position,
  void _startSimulation() {
    final routes = _mapController.preferences.routes;

    _mapController.preferences.routes.clearAllButMainRoute();

    if (routes.mainRoute == null) {
      _showSnackBar(context, message: "No main route available");
      return;
    }

    _alarmListener = AlarmListener(
      onOverlayItemAlarmsUpdated: () {
        // The overlay item alarm list containing the overlay items that are to be intercepted
        OverlayItemAlarmsList overlayItemAlarms =
            _alarmService!.overlayItemAlarms;

        // The overlay items and their distance from the reference position
        // Sorted ascending by distance from the current position
        List<OverlayItemPosition> items = overlayItemAlarms.items;

        if (items.isEmpty) {
          return;
        }

        // The closest overlay item and its associated distance
        OverlayItemPosition closestOverlayItem = items.first;

        setState(() {
          _closestOverlayItem = closestOverlayItem;
        });
      },
      // When the overlay item alarms are passed over
      onOverlayItemAlarmsPassedOver: () {
        setState(() {
          _closestOverlayItem = null;
        });
      },
    );

    // Set the alarms service with the listener
    _alarmService = AlarmService(_alarmListener!);

    _alarmService!.alarmDistance = 500;

    // Add the social reports overlay to be tracked by the alarm service
    _alarmService!.overlays.add(CommonOverlayId.safety.id);

    _navigationHandler = NavigationService.startSimulation(
      routes.mainRoute!,
      null,
      onNavigationInstruction: (instruction, events) {
        setState(() {
          _isSimulationActive = true;
        });
      },
      onDestinationReached: (landmark) {
        _stopSimulation();
        _cancelRoute();
      },
      onError: (error) {
        // If the navigation has ended or if an error occurred while navigating, remove routes and reset the closest alarm.
        setState(() {
          _isSimulationActive = false;
          _closestOverlayItem = null;
          _cancelRoute();
        });

        if (error != GemError.cancel) {
          _stopSimulation();
        }
        return;
      },
    );

    // Set the camera to follow position.
    _mapController.startFollowingPosition();
  }

  // Method for removing the routes from display,
  void _cancelRoute() {
    // Remove the routes from map.
    _mapController.preferences.routes.clear();

    if (_routingHandler != null) {
      // Cancel the navigation.
      RoutingService.cancelRoute(_routingHandler!);
      _routingHandler = null;
    }

    setState(() {
      _areRoutesBuilt = false;
    });
  }

  // Method to stop the simulation and remove the displayed routes,
  void _stopSimulation() {
    // Cancel the navigation.
    NavigationService.cancelNavigation(_navigationHandler!);
    _navigationHandler = null;

    _cancelRoute();

    setState(() => _isSimulationActive = false);
  }

  // Method to show a message in case the calculate route is not finished,
  void _showSnackBar(
    BuildContext context, {
    required String message,
    Duration duration = const Duration(hours: 1),
  }) {
    final snackBar = SnackBar(content: Text(message), duration: duration);

    ScaffoldMessenger.of(context).showSnackBar(snackBar);
  }
}

Flutter Examples

Maps SDK for Flutter Examples can be downloaded or cloned with Git.