Draw Shapes on Map

_{Estimated reading time: 3 minutes}

This example presents how to create a Flutter app that draws and displays shapes like polylines, polygons, and points on a map using Maps SDK for Flutter.

How It Works

The example app demonstrates the following features:

• Draw and display polylines, polygons, and points on the map.
• Handle user interaction through app bar buttons.

Polygon drawing	Polyline drawing	Points drawing

UI and Map Integration

This code defines the main UI elements, including the map and an app bar with buttons to draw polylines, polygons, and points on the map.

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Draw Shapes',
      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('Draw Shapes', style: TextStyle(color: Colors.white)),
        actions: [
          IconButton(
              onPressed: _onPolylineButtonPressed,
              icon: const Icon(
                Icons.adjust,
                color: Colors.white,
              )),
          IconButton(
              onPressed: _onPolygonButtonPressed,
              icon: const Icon(
                Icons.change_history,
                color: Colors.white,
              )),
          IconButton(
              onPressed: _onPointsButtonPressed,
              icon: const Icon(
                Icons.more_horiz,
                color: Colors.white,
              ))
        ],
      ),
      body: GemMap(
        key: ValueKey("GemMap"),
        onMapCreated: _onMapCreated,
        appAuthorization: projectApiToken,
      ),
    );
  }

Drawing and Displaying Shapes

This code snippet defines the methods to draw and display different shapes (polyline, polygon, points) on the map. Each method creates a MarkerCollection , adds markers with specific coordinates, and displays them on the map.

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

// Method to draw and center on a polyline
void _onPolylineButtonPressed() {
  // Create a marker collection
  final markerCollection = MarkerCollection(
      markerType: MarkerType.polyline, name: 'Polyline marker collection');

  // Set coordinates of marker
  final marker = Marker();
  marker.setCoordinates([
    Coordinates(latitude: 52.360495, longitude: 4.936882),
    Coordinates(latitude: 52.360495, longitude: 4.836882),
  ]);
  markerCollection.add(marker);

  _showMarkerCollectionOnMap(markerCollection);
}

// Method to draw and center on a polygon
void _onPolygonButtonPressed() {
  // Create a marker collection
  final markerCollection = MarkerCollection(
      markerType: MarkerType.polygon, name: 'Polygon marker collection');

  // Set coordinates of marker
  final marker = Marker();
  marker.setCoordinates([
    Coordinates(latitude: 52.340234, longitude: 4.886882),
    Coordinates(latitude: 52.300495, longitude: 4.936882),
    Coordinates(latitude: 52.300495, longitude: 4.836882),
  ]);
  markerCollection.add(marker);

  _showMarkerCollectionOnMap(markerCollection);
}

// Method to draw and center on points
void _onPointsButtonPressed() {
  // Create a marker collection
  final markerCollection = MarkerCollection(
      markerType: MarkerType.point, name: 'Points marker collection');

  // Set coordinates of marker
  final marker = Marker();
  marker.setCoordinates([
    Coordinates(latitude: 52.380495, longitude: 4.930882),
    Coordinates(latitude: 52.380495, longitude: 4.900882),
    Coordinates(latitude: 52.380495, longitude: 4.870882),
    Coordinates(latitude: 52.380495, longitude: 4.840882),
  ]);
  markerCollection.add(marker);

  _showMarkerCollectionOnMap(markerCollection);
}

Utility Functions

This utility method clears any previous markers on the map, then displays the new MarkerCollection and centers the map on the area containing the markers.

void _showMarkerCollectionOnMap(MarkerCollection markerCollection) {
  final settings = MarkerCollectionRenderSettings();

  // Clear previous markers from the map
  _mapController.preferences.markers.clear();

  // Show the current marker on map and center on it
  _mapController.preferences.markers
      .add(markerCollection, settings: settings);
  _mapController.centerOnArea(markerCollection.area);
}