Follow Position

This example demonstrates how to create a Flutter app that follows the device’s location on a map using gem_kit package, with an option to request location permissions if necessary.

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

Navigate to the follow_position directory within the Flutter examples directory. This is the project folder for this example.

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.

Run: flutter pub get

Configure the native parts:

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:

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    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 project pathname

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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
        }
    }
}

iOS

In the ios/Podfile configuration file, at the top, set the minimum ios platform version to 14 like this:

platform :ios, '14.0'

We recommend you to run these commands after you copy the gem_kit into your project: |flutter clean |flutter pub get |and |cd ios |pod install

Then run the project:

flutter run --debug

or

flutter run --release

App entry and initialization

const projectApiToken = String.fromEnvironment('GEM_TOKEN');

void main() {
  runApp(const MyApp());
}

This code initializes the projectApiToken with the required authorization token and launches the app.

How It Works

The example app demonstrates the following features:

• Requesting location permissions on Android and iOS, with automatic handling on web platforms.

• Setting the live data source for the map (typically the device’s GPS).

• Following the device’s location on the map with optional animation.

UI and Map Integration

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

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

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

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

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

  PermissionStatus _locationPermissionStatus = PermissionStatus.denied;
  bool _hasLiveDataSource = false;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple[900],
        title: const Text('Follow Position', style: TextStyle(color: Colors.white)),
        actions: [
          IconButton(
            onPressed: _onFollowPositionButtonPressed,
            icon: const Icon(Icons.location_searching_sharp, color: Colors.white),
          ),
        ],
      ),
      body: GemMap(onMapCreated: _onMapCreated, appAuthorization: projectApiToken),
    );
  }

This code sets up the app’s user interface, including a map and a button to follow the device’s position.

Handling Location Permissions and Following Position

// The callback for when the map is ready to use.
void _onMapCreated(GemMapController controller) async {
  // Save controller for further usage.
  _mapController = controller;
}

void _onFollowPositionButtonPressed() async {
  if (kIsWeb) {
    // On web platforms, permissions are handled differently.
    _locationPermissionStatus = PermissionStatus.granted;
  } else {
    // Request location permission on Android and iOS platforms.
    _locationPermissionStatus = await Permission.locationWhenInUse.request();
  }

  if (_locationPermissionStatus == PermissionStatus.granted) {
    // Set the live data source (GPS) if not already set.
    if (!_hasLiveDataSource) {
      PositionService.instance.setLiveDataSource();
      _hasLiveDataSource = true;
    }

    // Optionally, set an animation.
    final animation = GemAnimation(type: AnimationType.linear);

    // Start following the device's position.
    _mapController.startFollowingPosition(animation: animation);

    setState(() {});
  }
}

This code handles the process of requesting location permissions, setting the GPS as the live data source, and starting the map’s follow position mode.

Displaying Position Information

When the “Follow Position” button is pressed, the _onFollowPositionButtonPressed() callback is triggered. It requests location permission if it hasn’t been granted already, and sets the location data source to the device’s GPS sensor.

Once the permission is granted and the data source is set, the map will follow the device’s location, centering the camera on the current position. The follow position feature is disabled if the user interacts with the map, such as by panning, until the button is pressed again.

Flutter Examples

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