Add Markers

This example demonstrates how to create a Flutter app that displays a large number of markers on a map using Flutter and GemKit.

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 add_markers 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. 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

The example app demonstrates the following features:

• Display a large number of markers on the map.

import 'dart:math';
import 'dart:typed_data';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart' show rootBundle;
import 'package:gem_kit/core.dart';
import 'package:gem_kit/map.dart';

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

This imports the necessary packages, initializes GemKit, and sets up the main entry point of the app.

UI and Map Integration

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

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

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

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

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

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Colors.deepPurple[900],
        title: const Text('Hello Map', style: TextStyle(color: Colors.white)),
      ),
      body: GemMap(
        onMapCreated: _onMapCreated,
      ),
    );
  }

  Future<void> _onMapCreated(GemMapController controller) async {
    _mapController = controller;
    await addMarkers();
  }

This code sets up the basic structure of the app, including the map and the app bar, and initializes the map when it is created.

Adding and Displaying Markers

Future<void> addMarkers() async {
  final listPngs = await loadPngs();
  final ByteData imageData = await rootBundle.load('assets/pois/GroupIcon.png');
  final Uint8List imageBytes = imageData.buffer.asUint8List();

  Random random = Random();
  double minLat = 35.0; // Southernmost point of Europe
  double maxLat = 71.0; // Northernmost point of Europe
  double minLon = -10.0; // Westernmost point of Europe
  double maxLon = 40.0; // Easternmost point of Europe

  List<MarkerWithRenderSettings> markers = [];

  // Generate random coordinates for markers.
  for (int i = 0; i < 8000; ++i) {
    double randomLat = minLat + random.nextDouble() * (maxLat - minLat);
    double randomLon = minLon + random.nextDouble() * (maxLon - minLon);

    final marker = MarkerJson(
      coords: [Coordinates(latitude: randomLat, longitude: randomLon)],
      name: "POI $i",
    );

    final renderSettings = MarkerRenderSettings(
        image: GemImage(image: listPngs[random.nextInt(listPngs.length)], format: ImageFileFormat.png),
        labelTextSize: 2.0);

    final markerWithRenderSettings = MarkerWithRenderSettings(marker, renderSettings);

    markers.add(markerWithRenderSettings);
  }

  final settings = MarkerCollectionRenderSettings();
  settings.labelGroupTextSize = 2;
  settings.pointsGroupingZoomLevel = 35;
  settings.image = GemImage(image: imageBytes, format: ImageFileFormat.png);

  _mapController.preferences.markers.addList(list: markers, settings: settings, name: "Markers");
}

Future<List<Uint8List>> loadPngs() async {
  List<Uint8List> pngs = [];
  for (int i = 83; i < 183; ++i) {
    try {
      final ByteData imageData = await rootBundle.load('assets/pois/poi$i.png');
      final Uint8List png = imageData.buffer.asUint8List();
      pngs.add(png);
    } catch (e) {
      throw ("Error loading png $i");
    }
  }
  return pngs;
}

This code creates and adds a large number of markers to the map, generating random coordinates across Europe for demonstration purposes. It loads PNG images from assets to be used as marker icons.

Flutter Examples

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