https://flutterigniter.com/checking-null-aware-operators-dart/

Null check operator used on a null value

These links say that if the value can be null then we can use ?? operator to assign a value to it. I tried it, it still shows the same error:

This is the data structure.

main.dart

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

BigData bigDataFromJson(String str) => BigData.fromJson(json.decode(str));

class BigData {
  BigData({
    this.data,
  });
  Data? data;

  factory BigData.fromJson(Map<String, dynamic> json) => BigData(
        data: Data.fromJson(json["data"]),
      );

  Map<String, dynamic> toJson() => {
        "data": data!.toJson(),
      };
}

class Data {
  Data({
    this.lockoutDetails,
  });

  bool? lockoutDetails;

  factory Data.fromJson(Map<String, dynamic> json) => Data(
        lockoutDetails: json["lockout_details"],
      );

  Map<String, dynamic> toJson() => {
        "lockout_details": lockoutDetails,
      };
}

Here from the default application of Flutter starts:

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {  
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

Here I have used the variable lockoutDetails from the above datastructures and it shows the error null check operator used on a null value.

class _MyHomePageState extends State<MyHomePage> {
  BigData d = BigData();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Center(
      child:       
        d.data!.lockoutDetails ?? true
          ? const Text(
              'AAA',
            )
          : Container(),
    ));
  }
}

What is the way to correct it?

CodePudding user response：

you can use ? instead of ! which means that it may or maynot be null. If you add ! you are mentioning that its not null but the value is unknown

d.data?.lockoutDetails ?? true

CodePudding user response：

d.data is null in this case, you can replace

 d.data!.lockoutDetails ?? true

with

 d.data?.lockoutDetails ?? true

CodePudding user response：

Your d.data is null. For test run use d.data?.lockoutDetails.

Think to set data for to have value.