01. Flutter Google Maps Marker

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:provider/provider.dart';
import 'package:sizer/sizer.dart';

class GoogleMapsMarkerNotifier extends ChangeNotifier {
  final List<Marker> _markers = [];

  bool isSoloMarker = false;

  addNewMarker({required LatLng latLng}) {
    if (isSoloMarker) {
      _markers.clear();
      Marker marker = Marker(
          position: LatLng(latLng.latitude, latLng.longitude),
          markerId: MarkerId(latLng.toString()));
      _markers.add(marker);
      notifyListeners();
    } else {
      Marker marker = Marker(
          position: LatLng(latLng.latitude, latLng.longitude),
          markerId: MarkerId(latLng.toString()));
      _markers.add(marker);
      notifyListeners();
    }
  }

  setSoloMarker() {
    isSoloMarker = !isSoloMarker;
    notifyListeners();
  }

  clearMarkers() {
    _markers.clear();
    notifyListeners();
  }
}

class GoogleMapsMarkerExample extends StatelessWidget {
  const GoogleMapsMarkerExample({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    Completer<GoogleMapController> _controller = Completer();

    GoogleMapsMarkerNotifier googleMapsMarkerNotifier(
            {required bool renderUI}) =>
        Provider.of<GoogleMapsMarkerNotifier>(context, listen: renderUI);

    return Sizer(builder: ((context, orientation, deviceType) {
      return MaterialApp(
        debugShowCheckedModeBanner: false,
        home: Scaffold(
          floatingActionButtonLocation:
              FloatingActionButtonLocation.centerDocked,
          floatingActionButton: SizedBox(
            child: Column(mainAxisAlignment: MainAxisAlignment.end, children: [
              CustomRoundedButton(
                  onTap: () {
                    googleMapsMarkerNotifier(renderUI: false).setSoloMarker();
                  },
                  backgroundColor:
                      googleMapsMarkerNotifier(renderUI: true).isSoloMarker
                          ? Colors.deepOrangeAccent
                          : KConstantColors.blueColor,
                  label: googleMapsMarkerNotifier(renderUI: true).isSoloMarker
                      ? "Single mode"
                      : "Multiple mode",
                  height: 5,
                  width: 40),
              vSizedBox1,
              if (googleMapsMarkerNotifier(renderUI: true)._markers.isNotEmpty)
                CustomRoundedButton(
                    onTap: () {
                      googleMapsMarkerNotifier(renderUI: false).clearMarkers();
                    },
                    backgroundColor: KConstantColors.bgColorFaint,
                    label: "Clear markers",
                    height: 5,
                    width: 40),
            ]),
          ),
          appBar: AppBar(
              backgroundColor: KConstantColors.bgColorFaint,
              title: Text("Google maps markers",
                  style: KCustomTextStyle.kBold(context, 14))),
          backgroundColor: KConstantColors.bgColor,
          body: GoogleMap(
              mapType: MapType.hybrid,
              onTap: (latln) {
                googleMapsMarkerNotifier(renderUI: false)
                    .addNewMarker(latLng: latln);
              },
              markers: Set<Marker>.from(
                  googleMapsMarkerNotifier(renderUI: true)._markers.toList()),
              onMapCreated: (GoogleMapController controller) {
                _controller.complete(controller);
              },
              initialCameraPosition: const CameraPosition(
                  zoom: 16, target: LatLng(28.7041, 77.1025))),
        ),
      );
    }));
  }
}