Follow position

In this guide you will learn how to activate follow position, that is, cause the map to be centered on the actual location of the phone/device.

Location permission is required, and requested if not previously granted.

Setup

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

Prerequisites

It is required that you complete the Environment Setup - Flutter Examples guide before starting this guide.

Build and run

Start a terminal/command prompt and go to the follow_position directory, within the flutter examples directory - that is the name of this 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:

Web browser

flutter run

If such a question appears, select the chrome browser; in the above example, press 2.

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

Then build the apk:

flutter build apk --debug

or

flutter build apk --release

the apk file is located in the build/app/outputs/apk/debug or build/app/outputs/apk/release subdirectory, for debug or release build respectively, within the current project directory, such as center_coordinates

The apk file name is app-release.apk or app-debug.apk

You can copy the apk to an android device using adb, for example:

adb push app-release.apk sdcard

And then click on the apk in the file browser on the device to install and run it.

iOS

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

platform :ios, '13.0'

Run pod install in the [ios folder] ./ios/

Then go back to the repository root folder and type flutter build ios to build a Runner.app.

Type flutter run to build and run on an attached device.

You can open the <path/to>/ios/Runner.xcworkspace project in Xcode and execute and debug from there.

How it works

In the example project directory, such as center_coordinates, there is a text file named pubspec.yaml which contains project configuration and dependencies. The most important lines from this file are shown here:

name: center_coordinates
description: A Flutter example using Maps SDK for Flutter.

version: 1.0.0+1

environment:
  sdk: '>=3.0.5 <4.0.0'

dependencies:
  flutter:
    sdk: flutter
  gem_kit:
    path: plugins/gem_kit

  permission_handler: ^11.3.1

  cupertino_icons: ^1.0.2

  dev_dependencies:
    flutter_test:
      sdk: flutter

    flutter_lints: ^3.0.2

# The following section is specific to Flutter packages.
flutter:
  uses-material-design: true

The project must have a name and version. The dependencies list the Flutter SDK, and the gem_kit, Maps for Flutter SDK.

The source code is in example_pathname/lib/main.dart Replace example_pathname with the actual example path name, such as center_coordinates

import 'package:gem_kit/core.dart';
import 'package:gem_kit/map.dart';
import 'package:gem_kit/sense.dart';

import 'package:permission_handler/permission_handler.dart';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart' hide Route;

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

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

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

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

  void _onFollowPositionButtonPressed() async {
    if (kIsWeb) {
      // On web platform permission are handled differently than other platforms.
      // The SDK handles the request of permission for location.
      _locationPermissionStatus = PermissionStatus.granted;
    } else {
      // For Android & iOS platforms, permission_handler package is used to ask for permissions.
      _locationPermissionStatus = await Permission.locationWhenInUse.request();
    }

    if (_locationPermissionStatus == PermissionStatus.granted) {
      // After the permission was granted, we can set the live data source (in most cases the GPS).
      // The data source should be set only once, otherwise we'll get -5 error.
      if (!_hasLiveDataSource) {
        PositionService.instance.setLiveDataSource();
        _hasLiveDataSource = true;
      }

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

      // Calling the start following position SDK method.
      _mapController.startFollowingPosition(animation: animation);

      setState(() {});
    }
  }
}

The dart material package is imported, as well as the required gem_kit packages, and the permission_handler package, to request location permission from the user, if not previously granted.

When the follow position button is pressed, the _onFollowPositionButtonPressed() callback is invoked, which requests location permission, if not previously granted.

Then it sets the location data source, if not previously set - this is the GPS sensor on the phone/device.

Finally, using an animation, the map is centered on the location of the phone/device:

_mapController.startFollowingPosition(animation: animation);

If the user pans the map, the follow position is deactivated, and the device location is no longer followed by the camera, until the button is pressed again.

Flutter Examples

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