Non-nullable instance field 'arCoreController' must be initialized - flutter

Question

Good day! I am new to Flutter but I was trapped in the problem to make an AR app
I have almost been frustrated all day because of these problems...
Dart Analysis keeps saying this below...
Non-nullable instance field ['Ar_controller'] must be initialized in flutter. My whole day wasted due to this and tomorrow is my presentation. Please help me out as soon as possible
really appreciate it in advance.
import 'dart:typed_data';
import 'package:flutter_auth_ui/armodelselect.dart';
import 'package:arcore_flutter_plugin/arcore_flutter_plugin.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:network_image_to_byte/network_image_to_byte.dart';
import 'package:vector_math/vector_math_64.dart' as vector;
import 'armodelselect.dart';
class arviewpage extends StatefulWidget {
objmodel modeldes;
arviewpage(this.modeldes);
#override
_arviewpageState createState() => _arviewpageState(this.modeldes);
}
class _arviewpageState extends State<arviewpage> {
_arviewpageState(this.modeldes);
void initstate(){
super.initState();
}
List<double> cubesize;
objmodel modeldes;
ArCoreController arCoreController;
Uint8List byteImage,byteImage1;
Future<bool> _onWillPop() async {
Navigator.of(context).pop(true);
return true;
}
#override
Widget build(BuildContext context) {
return WillPopScope(
onWillPop: _onWillPop,
child: Scaffold(
appBar: AppBar(
title: const Text('Xperience'),
),
body: ArCoreView(
onArCoreViewCreated: _onArCoreViewCreated,
),
),
);
}
//functions::::::::::::::::::
void _onArCoreViewCreated(ArCoreController controller) {
arCoreController = controller;
if(modeldes.type=='sphere'){
_addsphere();
}
else if(modeldes.type=="sphere2"){
_addmoonearth();
}
else if(modeldes.type=='cube'){
_addCube();
}
}
//convert image to byteimage
Future<Uint8List> _networkImageToByte(String imageaddress,String imageaddress1) async {
byteImage = await networkImageToByte(imageaddress);
if(imageaddress1!="0"){
byteImage1=await networkImageToByte(imageaddress1);
}
return byteImage;
}
//convert cube size to double
List<String> convertStringtodoublearr(String size){
var cubesize=size.split(",");
for(int i=0;i<cubesize.length;i++){
this.cubesize[i]=double.parse(cubesize[i]);
}
return cubesize;
}
//sphere ar model implementation
Future _addsphere() async {
await _networkImageToByte(modeldes.img_url,modeldes.explain);
//description ar model:::::::::::::::::::::::::::::::
final material = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
//metallic: 1.0,
textureBytes: byteImage1,
);
final cube = ArCoreCube(
materials: [material],
size: vector.Vector3(0.5,0.2,0.1)
);
final node = ArCoreNode(
shape: cube,
position: vector.Vector3(0,-0.4,0.5),
);
//sphere texture model ::::::::::::::::::::::::::::::::::::
final eamaterial = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
textureBytes: byteImage,
);
final sphere = ArCoreSphere(
materials: [eamaterial],
radius: double.parse(modeldes.size[0]),
);
final eanode = ArCoreNode(
shape: sphere,
position: vector.Vector3(0,0,-1),
children: modeldes.explain=="0"?[]:[node],
);
arCoreController.addArCoreNode(eanode);
}
//cube ar model implementation
Future _addCube() async{
await _networkImageToByte(modeldes.img_url,modeldes.explain);
//description ar model::::::::::::::::::::::::::::::::::::
final material = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
//metallic: 1.0,
textureBytes: byteImage1,
);
final cube = ArCoreCube(
materials: [material],
size: vector.Vector3(0.5,0.2,0.1)
);
final node = ArCoreNode(
shape: cube,
position: vector.Vector3(0,-0.4,0.5),
);
//cube texture model ::::::::::::::::::::::::::::::::::;
final cube_material = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
//metallic: 1.0,
textureBytes: byteImage,
);
final cube_cube = ArCoreCube(
materials: [cube_material],
size: vector.Vector3(double.parse(modeldes.size[0]),double.parse(modeldes.size[1]),double.parse(modeldes.size[2])),
);
final cube_node = ArCoreNode(
shape: cube_cube,
children: modeldes.explain=="0"?[]:[node],
position: vector.Vector3(0,0,-1),
);
arCoreController.addArCoreNode(cube_node);
}
Future _addmoonearth() async {
await _networkImageToByte(modeldes.img_url,modeldes.explain);
//description ar model:::::::::::::::::::::::::::::::
final material = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
//metallic: 1.0,
textureBytes: byteImage1,
);
final moon = ArCoreSphere(
materials: [material],
radius: 0.05,
);
final node = ArCoreNode(
shape: moon,
position: vector.Vector3(0.2,0.3,0.5),
);
//sphere texture model ::::::::::::::::::::::::::::::::::::
final eamaterial = ArCoreMaterial(
metallic: 1,
color: Colors.blue,
textureBytes: byteImage,
);
final sphere = ArCoreSphere(
materials: [eamaterial],
radius: double.parse(modeldes.size[0]),
);
final eanode = ArCoreNode(
shape: sphere,
position: vector.Vector3(0,0,-1),
children: modeldes.explain=="0"?[]:[node],
);
arCoreController.addArCoreNode(eanode);
}
#override
void dispose() {
arCoreController.dispose();
super.dispose();
}
}

Answer 1

If some variable is not initialized at definition,
you need to 'late' keyword.
https://dart.dev/null-safety/understanding-null-safety#lazy-initialization
...
late ArCoreController arCoreController;
...

Answer 2

Copy your package name which requires null safety
Go to pub.dev, search for the package name.
Look for similar package with null safety tag.
Copy package name from pub.dev
Paste in your pubspec.yaml in place of old package name.
Click on download button if working in VS Code or type in the command
flutter pub get