Offline Routing

In this guide, you will learn how to implement offline routing functionality using the gem_kit package. This example demonstrates how to download a map for offline use, disable internet access, and calculate routes offline.

Setup

First, get an API key token, see the Getting Started guide.

Prerequisites

Make sure you completed the Environment Setup - Flutter Examples guide before starting this guide.

Build and Run

Start a terminal/command prompt and navigate to the offline_routing directory within the Flutter examples directory. This is the name of the example project.

Note - the gem_kit directory containing the Maps SDK for Flutter should be in the plugins directory of the example, e.g. example_pathname/plugins/gem_kit - see the environment setup guide above. Replace example_pathname with the actual example path name, such as address_search

Download project dependencies:

flutter upgrade

run the following terminal commands in the project directory, where the pubspec.yaml file is located:

flutter clean

flutter pub get

Run the example:

Android

First, verify that the ANDROID_SDK_ROOT environment variable is set to the root path of your android SDK.

In android/build.gradle add the maven {} block as shown, within the allprojects {} block, for both debug and release builds, without the line numbers, those are for reference:

allprojects {
    repositories {
        google()
        mavenCentral()
        maven {
           url "${rootDir}/../plugins/gem_kit/android/build"
        }
    }
}

in android/app/build.gradle within the android {} block, in the defaultConfig {} block, the android SDK version minSdk must be set as shown below.

Additionally, for release builds, in android/app/build.gradle, within the android {} block, add the buildTypes {} block as shown:

Replace example_pathname with the actual example pathname, such as center_coordinates

android {
    defaultConfig {
        applicationId "com.magiclane.gem_kit.examples.example_pathname"
        minSdk 21
        targetSdk flutter.targetSdk
        versionCode flutterVersionCode.toInteger()
        versionName flutterVersionName
    }
    buildTypes {
        release {
            minifyEnabled false
            shrinkResources false

            // TODO: Add your own signing config for the release build.
            // Signing with the debug keys for now, so `flutter run --release` works.
            signingConfig signingConfigs.debug
        }
    }
}

Then run the project:

flutter run --debug

or

flutter run --release

iOS

In the ios/Podfile configuration text file, at the top, set the minimum ios platform to 13 like this:

platform :ios, '13.0'

Then run the project:

flutter run --debug

or

flutter run --release

How it Works

This example demonstrates how to use the gem_kit package to download a map for offline use, disable internet access, and calculate routes offline.

Import Necessary Packages

First, import the required packages in your Dart code.

import 'package:gem_kit/core.dart';
import 'package:gem_kit/map.dart';
import 'package:gem_kit/routing.dart';
import 'package:flutter/material.dart' hide Route;

Initialize GemKit

In the main function, initialize GemKit with your project API token.

Future<void> main() async {
  const projectApiToken = String.fromEnvironment('GEM_TOKEN');
  await GemKit.initialize(appAuthorization: projectApiToken);
  runApp(const MyApp());
}

Build the Main Application

Define the main application widget, MyApp.

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

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

Handle Maps and Routes in the Stateful Widget

Create the stateful widget, MyHomePage, which will handle the map and routing functionality.

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

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

Define State Variables and Methods

Within _MyHomePageState, define the necessary state variables and methods to interact with the map and manage routes.

class _MyHomePageState extends State<MyHomePage> {
  late GemMapController _mapController;
  bool _areRoutesBuilt = false;
  TaskHandler? _routingHandler;
  bool _isDownloaded = false;
  double _downloadProgress = 0;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple[900],
        title: const Text(
          'Offline Routing',
          style: TextStyle(color: Colors.white),
        ),
        actions: [
          if (!_isDownloaded && _downloadProgress != 0)
            Container(
              width: 20,
              height: 20,
              margin: const EdgeInsets.only(right: 10.0),
              child: const Center(
                child: CircularProgressIndicator(color: Colors.white),
              ),
            ),
          if (!_isDownloaded && _downloadProgress == 0)
            IconButton(
              onPressed: _setOfflineMap,
              icon: const Icon(
                Icons.download,
                color: Colors.white,
              ),
            ),
          if (_routingHandler == null && !_areRoutesBuilt && _isDownloaded)
            IconButton(
              onPressed: () => _onBuildRouteButtonPressed(context),
              icon: const Icon(
                Icons.route,
                color: Colors.white,
              ),
            ),
          if (_routingHandler != null)
            IconButton(
              onPressed: _onCancelRouteButtonPressed,
              icon: const Icon(
                Icons.stop,
                color: Colors.white,
              ),
            ),
          if (_areRoutesBuilt)
            IconButton(
              onPressed: _onClearRoutesButtonPressed,
              icon: const Icon(
                Icons.clear,
                color: Colors.white,
              ),
            ),
        ],
      ),
      body: GemMap(onMapCreated: _onMapCreated),
    );
  }

  void _onMapCreated(GemMapController controller) async {
    _mapController = controller;
    SdkSettings.setAllowOffboardServiceOnExtraChargedNetwork(
        ServiceGroupType.contentService, true);
  }

  void _onBuildRouteButtonPressed(BuildContext context) {
    final departureLandmark =
        Landmark.withLatLng(latitude: 42.49720, longitude: 1.50498);
    final destinationLandmark =
        Landmark.withLatLng(latitude: 42.51003, longitude: 1.53400);
    final routePreferences = RoutePreferences();

    _showSnackBar(context, message: "The route is being calculated.");

    _routingHandler = RoutingService.calculateRoute(
        [departureLandmark, destinationLandmark], routePreferences,
        (err, routes) {
      _routingHandler = null;
      ScaffoldMessenger.of(context).clearSnackBars();

      if (err == GemError.success) {
        final routesMap = _mapController.preferences.routes;
        for (final route in routes!) {
          routesMap.add(route, route == routes.first, label: route.getMapLabel());
        }
        _mapController.centerOnRoutes(routes);
        setState(() {
          _areRoutesBuilt = true;
        });
      }
    });

    setState(() {});
  }

  void _onClearRoutesButtonPressed() {
    _mapController.preferences.routes.clear();
    setState(() {
      _areRoutesBuilt = false;
    });
  }

  void _onCancelRouteButtonPressed() {
    if (_routingHandler != null) {
      RoutingService.cancelRoute(_routingHandler!);
      setState(() {
        _routingHandler = null;
      });
    }
  }

  Future<List<ContentStoreItem>> _getMaps() async {
    Completer<List<ContentStoreItem>> mapsList =
        Completer<List<ContentStoreItem>>();

    ContentStore.asyncGetStoreContentList(ContentType.roadMap,
        (err, items, isCached) {
      if (err == GemError.success && items != null) {
        mapsList.complete(items);
      }
    });
    return mapsList.future;
  }

  void _setOfflineMap() {
    final localMaps = ContentStore.getLocalContentList(ContentType.roadMap);

    if (localMaps.where((map) => map.name == 'Andorra').isNotEmpty) {
      setState(() {
        _isDownloaded = true;
      });
      SdkSettings.setAllowConnection(false);
      return;
    }

    _getMaps().then((maps) {
      _downloadProgress = maps[4].downloadProgress.toDouble();
      _downloadMap(maps[4]);
    });
  }

  void _downloadMap(ContentStoreItem map) {
    map.asyncDownload(_onMapDownloadFinished,
        onProgressCallback: _onMapDownloadProgressUpdated,
        allowChargedNetworks: true);
  }

  void _onMapDownloadProgressUpdated(int progress) {
    setState(() => _downloadProgress = progress.toDouble());
  }

  void _onMapDownloadFinished(GemError err) {
    if (err == GemError.success) {
      SdkSettings.setAllowConnection(false);
      setState(() => _isDownloaded = true);
    }
  }

  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);
  }
}

Define Extension for Route Label

Define an extension to format the route label displayed on the map.

extension RouteExtension on Route {
  String getMapLabel() {
    final totalDistance = getTimeDistance().unrestrictedDistanceM +
        getTimeDistance().restrictedDistanceM;
    final totalDuration =
        getTimeDistance().unrestrictedTimeS + getTimeDistance().restrictedTimeS;

    return '${_convertDistance(totalDistance)} \n${_convertDuration(totalDuration)}';
  }

  String _convertDistance(int meters) {
    if (meters >= 1000) {
      double kilometers = meters / 1000;
      return '${kilometers.toStringAsFixed(1)} km';
    }
    return '$meters m';
  }

  String _convertDuration(int seconds) {
    if (seconds >= 3600) {
      int hours = seconds ~/ 3600;
      int minutes = (seconds % 3600) ~/ 60;
      return '${hours}h ${minutes}m';
    } else if (seconds >= 60) {
      int minutes = seconds ~/ 60;
      return '${minutes}m';
    }
    return '${seconds}s';
  }
}

Flutter Examples

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