Question 136167 in Visual Studio Code Question posted in
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Visual Studio Code – Error while initializing marker in flutter

    // ignore_for_file: use_key_in_widget_constructors, prefer_final_fields, prefer_const_constructors, duplicate_ignore, camel_case_types, unnecessary_new, unnecessary_this, unnecessary_null_comparison

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:location/location.dart';

class map extends StatefulWidget {
  @override
  State<map> createState() => mapState();
}

class mapState extends State<map> {
  late GoogleMapController _controller;
  LatLng? latlng;
  late StreamSubscription _locationSubscription;
  Location _locationTracker = Location();
  Marker marker ;
  Circle circle;
  // ignore: prefer_const_constructors
  static CameraPosition _kGooglePlex = CameraPosition(
    target: LatLng(37.42796133580664, -122.085749655962),
    zoom: 15,
  );

  Future<Uint8List> getMarker() async {
    ByteData byteData = await DefaultAssetBundle.of(context).load("assets/car_icon.png");
    return byteData.buffer.asUint8List();
  }
  
  static final CameraPosition _kLake = CameraPosition(
      bearing: 192.8334901395799,
      target: LatLng(37.43296265331129, -122.08832357078792),
      tilt: 59.440717697143555,
      zoom: 19.151926040649414);

  void updateMarkerAndCircle(LocationData newLocalData, Uint8List imageData) {
    LatLng latlng = LatLng(newLocalData.latitude!, newLocalData.longitude!);
    this.setState(() {
      marker = Marker(
          markerId: MarkerId("home"),
          position: latlng,
          rotation: newLocalData.heading!,
          draggable: false,
          zIndex: 2,
          flat: true,
          anchor: Offset(0.5, 0.5),
          icon: BitmapDescriptor.fromBytes(imageData));
      circle = Circle(
          circleId: CircleId("car"),
          radius: newLocalData.accuracy!,
          zIndex: 1,
          strokeColor: Colors.blue,
          center: latlng,
          fillColor: Colors.blue.withAlpha(70));
    });
  }
    void getCurrentLocation() async {
    try {

      Uint8List imageData = await getMarker();
      var location = await _locationTracker.getLocation();

      updateMarkerAndCircle(location, imageData);

      if (_locationSubscription != null) {
        _locationSubscription.cancel();
      }


      _locationSubscription = _locationTracker.onLocationChanged.listen((newLocalData) {
        if (_controller != null) {
          _controller.animateCamera(CameraUpdate.newCameraPosition(new CameraPosition(
              bearing: 192.8334901395799,
              target: LatLng(newLocalData.latitude!, newLocalData.longitude!),
              tilt: 0,
              zoom: 18.00)));
          updateMarkerAndCircle(newLocalData, imageData);
        }
      });

    } on PlatformException catch (e) {
      if (e.code == 'PERMISSION_DENIED') {
        debugPrint("Permission Denied");
      }
    }
  }

  @override
  void dispose() {
    if (_locationSubscription != null) {
      _locationSubscription.cancel();
    }
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GoogleMap(
        mapType: MapType.hybrid,
        myLocationButtonEnabled: true,
        myLocationEnabled: true,
        initialCameraPosition: _kGooglePlex,
        markers: Set.of((marker != null) ? [marker] : []),
        circles: Set.of((circle != null) ? [circle] : []),
        onMapCreated: (GoogleMapController controller) {
          _controller = controller;
        },
      ),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      floatingActionButton: FloatingActionButton.extended(
        onPressed: getCurrentLocation,
        label: Text('To the lake!'),
        icon: Icon(Icons.location_searching),
      ),
    );
  }
}

This is original code in which i’m facing the error. when i define Marker marker like this it says maker should be initialise , when i define it like late Marker marker then code dosen’t shows any error but in app it says LateInitialization error : Field marker has not been initialized, and third one when i define it like Marker? marker , while passinf the value marker in GoogleMap function like this markers: Set.of((marker != null) ? [marker] : []) shows the error The element type 'Circle?' can't be assigned to the list type 'Circle'.
im using vscode and dependencies are

google_maps_flutter: ^2.2.0

location: ^4.4.0

Tags:

2

Answers


  1. 0

    I suggest that you change the declaration from either

    late Marker marker;
// or
Marker marker;

    to

    // Please use null safety code syntax
Marker? marker;

    As you already perform a null check on the build method, this should work.

    EDIT:

    Since your Marker instance should be a nullable now, then you can rephrase the line where you assign the markers on GoogleMap constructor like this

    GoogleMap(
  // ...other arguments
  markers: marker != null ? { marker, } : {}, // if marker is not null, assign a Set with single element, else assign an empty Set
)
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  2. 0

    Change marker to this:

    final Set<Marker> _markers = {};

    then in your updateMarkerAndCircle, do this:

    _markers.add(Marker(
          markerId: MarkerId("home"),
          position: latlng,
          rotation: newLocalData.heading!,
          draggable: false,
          zIndex: 2,
          flat: true,
          anchor: Offset(0.5, 0.5),
          icon: BitmapDescriptor.fromBytes(imageData)));

    then in your GoogleMap widget, do this:

    GoogleMap(
        mapType: MapType.hybrid,
        myLocationButtonEnabled: true,
        myLocationEnabled: true,
        initialCameraPosition: _kGooglePlex,
        markers: _markers,
        circles: Set.of((circle != null) ? [circle] : []),
        onMapCreated: (GoogleMapController controller) {
          _controller = controller;
        },
      )
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