The following _CastError was thrown building Container: Null check operator used on a null value

Question

I got this error when I run my simple flutter APP. I could not figure out why this error occurred.

Error

Null check operator used on a null value

import 'package:flutter/material.dart';
import 'package:get/get.dart';

import 'package:star_book/src/controller/mapDataController.dart';

import 'package:star_book/src/model/app_settings.dart';
import 'package:star_book/src/model/category.dart';
import 'package:star_book/src/model/map_data.dart';

class MapInformationPage extends StatefulWidget {
  late final String selectedMap;

  MapInformationPage(this.selectedMap);

  @override
  _MapInformationPageState createState() => _MapInformationPageState();
}

class _MapInformationPageState extends State<MapInformationPage> {
  final _mapController = Get.put(MapDataController());
  late final MapData mapData;
  late AppSettings _appSettings;
  late List<Category> _favoriteIcons;
  late int _favoriteIconsIndex;

  @override
  void initState() {
    super.initState();
    _appSettings = AppSettings();
    _favoriteIcons = [
      Category(Icons.favorite_border, Colors.black),
      Category(Icons.favorite, Colors.red),
    ];
    _favoriteIconsIndex = 0;
    _mapController.selectedMapData(widget.selectedMap);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        leading: IconButton(
          onPressed: () {
            Get.back();
          },
          icon: Icon(Icons.arrow_back),
          iconSize: 24,
        ),
        backgroundColor: _appSettings.appBarAndNavColor,
      ),
      body: Container(
        width: _appSettings.appWidth * 0.9,
        height: _appSettings.appHeight - _appSettings.appBarHeight,
        child: ListView(children: [
          Container(
            child: GetBuilder(
              builder: (_) {
                return Text(
                  'map > star1 >' + _mapController.mapData.name.toString(),
                  style: TextStyle(fontSize: 20),
                );
              },
            ),
          ),
        ]),
      ),
    );
  }
}

My flutter doctor output

[√] Flutter (Channel stable, 2.2.3, on Microsoft Windows [Version 10.0.19043.1165], locale ko-KR)
• Flutter version 2.2.3 at C:\Program Files\flutter
• Framework revision f4abaa0735 (8 weeks ago), 2021-07-01 12:46:11 -0700
• Engine revision 241c87ad80
• Dart version 2.13.4

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.3) • Android SDK at C:\Users\HOME\AppData\Local\Android\sdk • Platform android-30, build-tools 29.0.3 • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01) • All Android licenses accepted.

[√] Chrome - develop for the web • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.1.0) • Android Studio at C:\Program Files\Android\Android Studio • Flutter plugin can be installed from: https://plugins.jetbrains.com/plugin/9212-flutter • Dart plugin can be installed from: https://plugins.jetbrains.com/plugin/6351-dart • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code (version 1.59.1) • VS Code at C:\Users\HOME\AppData\Local\Programs\Microsoft VS Code • Flutter extension version 3.25.0

[√] Connected device (3 available) • sdk gphone x86 (mobile) • emulator-5554 • android-x86 • Android 11 (API 30) (emulator) • Chrome (web) • chrome • web-javascript • Google Chrome 92.0.4515.159 • Edge (web) • edge • web-javascript • Microsoft Edge 92.0.902.78

Can anyone provide a solution for this?

score 0 · Answer 1 · answered Aug 27 '21 at 03:33

0

It's most probably you are using SDK of flutter which employs null safety. Edit your pubspec.yaml with fluuter sdk less than 2.12 or ensure null safety in your code.

answered Aug 27 '21 at 03:33

Shashikant Verma

31
4

score 0 · Accepted Answer · answered Aug 27 '21 at 03:59

Normally, "Null check operator used on a null value" is throw when

var v = null;
var s = v!.value; <--"Null check operator used on a null value"

You can check the simple flutter APP codes.

Also, this may help: Null check operator used on a null value

The following _CastError was thrown building Container: Null check operator used on a null value

2 Answers2