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

I found myself on this exact stackoverflow page multiple times this year. So, I decided to go and make my first Flutter Package and created this. If your objective is to add a simple and clear text to map marker, this would do it.

https://pub.dev/packages/label_marker

Usage

markers.addLabelMarker(LabelMarker(
    label: "TextToShow",
    markerId: MarkerId("idString"),
    position: LatLng(10.0, 11.0),
    backgroundColor: Colors.green,
    )).then((value) {
    setState(() {});
    },
);