Custom markers with Flutter Google Maps plugin

Question

Is there a way to display custom markers with the official Flutter Google Maps plugin on the map? Can't find any way to do it based on the documentation.

Answer 1

You can use Flutter widgets for custom markers with this class

import 'package:flutter/material.dart';
import 'dart:typed_data';
import 'package:flutter/rendering.dart';
import 'dart:ui' as ui;

/// This just adds overlay and builds [_MarkerHelper] on that overlay.
/// [_MarkerHelper] does all the heavy work of creating and getting bitmaps
class MarkerGenerator {
  final Function(List<Uint8List>) callback;
  final List<Widget> markerWidgets;

  MarkerGenerator(this.markerWidgets, this.callback);

  void generate(BuildContext context) {
    WidgetsBinding.instance
        .addPostFrameCallback((_) => afterFirstLayout(context));
  }

  void afterFirstLayout(BuildContext context) {
    addOverlay(context);
  }

  void addOverlay(BuildContext context) {
    OverlayState overlayState = Overlay.of(context);

    OverlayEntry entry;
    entry = OverlayEntry(
        builder: (context) {
          return _MarkerHelper(
            markerWidgets: markerWidgets,
            callback: (List<Uint8List> bitmapList) {
                // Given callback function
                callback.call(bitmapList);
                
                // Remove marker widget stack from Overlay when finished
                entry.remove();
              },
          );
        },
        maintainState: true);

    overlayState.insert(entry);
  }
}

/// Maps are embeding GoogleMap library for Andorid/iOS  into flutter.
///
/// These native libraries accept BitmapDescriptor for marker, which means that for custom markers
/// you need to draw view to bitmap and then send that to BitmapDescriptor.
///
/// Because of that Flutter also cannot accept Widget for marker, but you need draw it to bitmap and
/// that's what this widget does:
///
/// 1) It draws marker widget to tree
/// 2) After painted access the repaint boundary with global key and converts it to uInt8List
/// 3) Returns set of Uint8List (bitmaps) through callback
class _MarkerHelper extends StatefulWidget {
  final List<Widget> markerWidgets;
  final Function(List<Uint8List>) callback;

  const _MarkerHelper({Key key, this.markerWidgets, this.callback})
      : super(key: key);

  @override
  _MarkerHelperState createState() => _MarkerHelperState();
}

class _MarkerHelperState extends State<_MarkerHelper> with AfterLayoutMixin {
  List<GlobalKey> globalKeys = [];

  @override
  void afterFirstLayout(BuildContext context) {
    _getBitmaps(context).then((list) {
      widget.callback(list);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Transform.translate(
          offset: Offset(MediaQuery.of(context).size.width, 0),
          child: Material(
            type: MaterialType.transparency,
            child: Stack(
              children: widget.markerWidgets.map((i) {
                final markerKey = GlobalKey();
                globalKeys.add(markerKey);
                return RepaintBoundary(
                  key: markerKey,
                  child: i,
                );
              }).toList(),
            ),
          ),
    );
  }

  Future<List<Uint8List>> _getBitmaps(BuildContext context) async {
    var futures = globalKeys.map((key) => _getUint8List(key));
    return Future.wait(futures);
  }

  Future<Uint8List> _getUint8List(GlobalKey markerKey) async {
    RenderRepaintBoundary boundary =
    markerKey.currentContext.findRenderObject();
    var image = await boundary.toImage(pixelRatio: 2.0);
    ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
    return byteData.buffer.asUint8List();
  }
}

/// AfterLayoutMixin
mixin AfterLayoutMixin<T extends StatefulWidget> on State<T> {
  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance
        .addPostFrameCallback((_) => afterFirstLayout(context));
  }

  void afterFirstLayout(BuildContext context);
}

usage example

import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:map_marker_sample/gist/Gist.dart';

class MapScreen extends StatefulWidget {
  @override
  _MapScreenState createState() => _MapScreenState();
}

class _MapScreenState extends State<MapScreen> {
  List<Marker> markers = [];

  @override
  Widget build(BuildContext context) {
    return Container(
        child: Stack(
          children: <Widget>[
            GoogleMap(
              initialCameraPosition:
                  CameraPosition(target: LatLng(45.811328, 15.975862), zoom: 8),
              markers: markers.toSet(),
            ),
          ],
        ),
    );
  }

  @override
  void initState() {
    super.initState();

    MarkerGenerator(markerWidgets(), (bitmaps) {
      setState(() {
        markers = mapBitmapsToMarkers(bitmaps);
      });
    }).generate(context);
  }

  List<Marker> mapBitmapsToMarkers(List<Uint8List> bitmaps) {
    List<Marker> markersList = [];
    bitmaps.asMap().forEach((i, bmp) {
      final city = cities[i];
      markersList.add(Marker(
          markerId: MarkerId(city.name),
          position: city.position,
          icon: BitmapDescriptor.fromBytes(bmp)));
    });
    return markersList;
  }
}

// Example of marker widget
Widget _getMarkerWidget(String name) {
  return Container(
    padding: EdgeInsets.symmetric(horizontal: 0, vertical: 0),
    child: Container(
      padding: EdgeInsets.symmetric(horizontal: 3, vertical: 1.5),
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(10),
        border: Border.all(color: Colors.black, width: 1),
        color: Colors.white,
        shape: BoxShape.rectangle,
      ),
      child: Text(
        name,
        style: TextStyle(fontSize: 14, color: Colors.black),
      ),
    ),
  );
}

// Example of backing data
List<City> cities = [
  City("Zagreb", LatLng(45.792565, 15.995832)),
  City("Ljubljana", LatLng(46.037839, 14.513336)),
  City("Novo Mesto", LatLng(45.806132, 15.160768)),
  City("Varaždin", LatLng(46.302111, 16.338036)),
  City("Maribor", LatLng(46.546417, 15.642292)),
  City("Rijeka", LatLng(45.324289, 14.444480)),
  City("Karlovac", LatLng(45.489728, 15.551561)),
  City("Klagenfurt", LatLng(46.624124, 14.307974)),
  City("Graz", LatLng(47.060426, 15.442028)),
  City("Celje", LatLng(46.236738, 15.270346))
];

List<Widget> markerWidgets() {
  return cities.map((c) => _getMarkerWidget(c.name)).toList();
}

class City {
  final String name;
  final LatLng position;

  City(this.name, this.position);
}

source Link: https://infinum.com/the-capsized-eight/creating-custom-markers-on-google-maps-in-flutter-apps

github repository :https://github.com/itsJoKr/markers_generator_sample