How to add extra into text into flutter google map custom marker?

try this :

 import 'package:flutter/material.dart';import 'package:google_maps_flutter/google_maps_flutter.dart';class MapsDemo extends StatefulWidget {  @override  State createState() => MapsDemoState();}class MapsDemoState extends State<MapsDemo> {  final Set<Marker> _markers = {};  void _onAddMarkerButtonPressed() {    print('in _onAddMarkerButtonPressed()');    setState(() {      _markers.add(Marker(        // This marker id can be anything that uniquely identifies each marker.        markerId: MarkerId("111"),        position: LatLng(30.666, 76.8127),        infoWindow: InfoWindow(          title: "bingo! This works",        ),        icon: BitmapDescriptor.defaultMarker,      ));    });    print('setState() done');  }  GoogleMapController mapController;  //Map<PermissionGroup, PermissionStatus> permissions = await PermissionHandler().requestPermissions([PermissionGroup.contacts]);import 'package:permission_handler/permission_handler.dart';  @override  Widget build(BuildContext context) {    return Scaffold(        body: Column(          children: <Widget>[            Container(              height: MediaQuery.of(context).size.height,              width: MediaQuery.of(context).size.width,              child: GoogleMap(                markers: _markers,                onMapCreated: (GoogleMapController controller) {                  mapController = controller;                },                initialCameraPosition:                    CameraPosition(target: LatLng(30.666, 76.8127), zoom: 15),              ),            ),          ],        ),        floatingActionButton: FloatingActionButton(onPressed: () {          print('in fab()');          double mq1 = MediaQuery.of(context).devicePixelRatio;          _onAddMarkerButtonPressed();          mapController.animateCamera(            CameraUpdate.newCameraPosition(              CameraPosition(                target: LatLng(30.666, 76.8127),                zoom: 15.0,              ),            ),          );        }));  }}

I kludged/solved this by creating a function which returned a , whose returned and resolved value I then passed in as the icon when initializing a Marker:

Sorry to say that I don't remember why I padded the method with the magic 40 and 20 constants. Probably calculated by visual test with what I was rendering at the time.

Future<BitmapDescriptor> createCustomMarkerBitmap(/* your args here */) async {PictureRecorder recorder = new PictureRecorder();Canvas c = new Canvas(recorder);/* Do your painting of the custom icon here, including drawing text, shapes, etc. */Picture p = recorder.endRecording();ByteData pngBytes = await (await p.toImage(    tp.width.toInt() + 40, tp.height.toInt() + 20))    .toByteData(format: ImageByteFormat.png);Uint8List data = Uint8List.view(pngBytes.buffer);return BitmapDescriptor.fromBytes(data);}

Then when creating the marker, you can pass in the BitmapDescriptor as the icon, like so:

createCustomMarkerBitmap(...).then((BitmapDescriptor bitmapDescriptor) {

_markers.add(new Marker(/* in addition to your other properties: */icon: bitmapDescriptor,));});

or:

BitmapDescriptor bitmapDescriptor = await createCustomMarkerBitmap(...);

Marker marker = Marker(/* in addition to your other properties: */icon: bitmapDescriptor);

Let me know if that helps. Gl!

I have found this answer for github issue