Null check operator used on a null value. The relevant error-causing widget was StreamBuilder

Question

hi every one hope you doing well I have a code to develop an app by flutter language but this error appears to me in list.dart. this list.dart file should display the posts from firebase with the images if there are.

and I don't know the answer

this is the code

import 'package:flutter/material.dart';
import 'package:insight_software/models/postModel.dart';
import 'package:insight_software/other_screen/userFunction.dart';
import 'package:provider/provider.dart';

import '../models/user.dart';

class ListPost extends StatefulWidget {
  ListPost({Key? key}) : super(key: key);

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

class _ListPostState extends State<ListPost> {
  UserService _userService = UserService();
  @override
  Widget build(BuildContext context) {
    List<postModel?> posts = Provider.of<List<postModel?>>(context);
    return ListView.builder(
      itemCount: posts.length,
      itemBuilder: (context, index) {
        final Post = posts[index];
        
        return StreamBuilder(
            stream: _userService.getUserInfo(Post!.creator),
            builder:
                (BuildContext context, AsyncSnapshot<UserModel?> snapshot) {
              // if (!snapshot.hasData) {
              //   return Center(child: CircularProgressIndicator());
              // }
              return ListTile(
                title: Padding(
                  padding: EdgeInsets.fromLTRB(0, 15, 0, 15),
                  child: Row(
                    children: [
                      snapshot.data!.profileImageUrl != ''
                          ? CircleAvatar(
                              radius: 20,
                              backgroundImage:
                                  NetworkImage(snapshot.data!.profileImageUrl))
                          : Icon(
                              Icons.person,
                              size: 30,
                            ),
                      SizedBox(width: 10),
                      Text(snapshot.data!.name),
                    ],
                  ),
                ),
                subtitle: Column(
                  crossAxisAlignment: CrossAxisAlignment.start,
                  children: [
                    Padding(
                      padding: EdgeInsets.fromLTRB(0, 15, 0, 15),
                      child: Column(
                        crossAxisAlignment: CrossAxisAlignment.start,
                        children: [
                          Text(Post.post),
                          SizedBox(height: 20),
                          Text(Post.timestamp.toDate().toString())
                        ],
                      ),
                    ),
                    Divider(),
                  ],
                ),
              );
            });
      },
    );
  }
}

who is knowing how I can solve this problem please help me.

my postModel class:

import 'package:cloud_firestore/cloud_firestore.dart';

class postModel {
  final String id;
  final String creator;
  final String post;
  final Timestamp timestamp;

  postModel(
      {required this.id,
      required this.creator,
      required this.post,
      required this.timestamp});
}

my userModel class:

class UserModel {
  final String id;
  final String bannerImageUrl;
  final String profileImageUrl;
  final String name;
  final String email;

  UserModel({
    required this.id,
    required this.bannerImageUrl,
    required this.profileImageUrl,
    required this.name,
    required this.email,
  });
}

and this is the getUserInfo

UserModel? _userFromFirebaseSnapshot(DocumentSnapshot snapshot) {
    return snapshot != null
        ? UserModel(
            id: snapshot.id,
            name: snapshot.get('First Name') ?? '',
            profileImageUrl: snapshot.get('profileImageUrl') ?? '',
            bannerImageUrl: snapshot.get('bannerImageUrl') ?? '',
            email: snapshot.get('email') ?? '',
          )
        : null;
  }

  Stream<UserModel?> getUserInfo(uid) {
    return FirebaseFirestore.instance
        .collection("Users")
        .doc(uid)
        .snapshots()
        .map(_userFromFirebaseSnapshot);
  }

Please write your 'postModel' & 'UserModel' Class. – M Karimi Feb 27 '22 at 05:07 — M Karimi, Feb 27 '22 at 05:07
I've updated my below answer according your Class. – M Karimi Feb 27 '22 at 05:34 — M Karimi, Feb 27 '22 at 05:34

M Karimi · Accepted Answer · 2022-02-27T05:33:41.163

0

This error occurs when you use a bang operator (!) on a nullable instance which wasn't initialized.

String? foo; // Nullable String

void main() {
  var len = foo!.length; // Runtime error: Null check operator used on a null value
}

For more details, you can see this answer.

So you can update your code:

stream: _userService.getUserInfo(Post!.creator),

with stream: _userService.getUserInfo(Post?.creator ?? ''),

and snapshot.data!.profileImageUrl != ''

with (snapshot.data?.profileImageUrl ?? '') != ''

and NetworkImage(snapshot.data!.profileImageUrl))

with NetworkImage(snapshot.data?.profileImageUrl) ?? '')

and Text(snapshot.data!.name),

with Text(snapshot.data?.name ?? ''),

edited Feb 27 '22 at 05:33

answered Feb 27 '22 at 05:09

M Karimi

1,991
1
17
34

thank you so much is working know❤️ – anoud Feb 27 '22 at 05:43
So please accept my answer by clicking tick mark next to the my answer if it solved your problem. – M Karimi Feb 27 '22 at 06:34
there is a small error that appears to me the name in this line Text(snapshot.data?.name ?? ''), should be displayed on the simulator but it its not – anoud Feb 27 '22 at 07:10
It's because that 'snapshot.data.name' is null so snapshot.data?.name ?? '' returns an empty String. – M Karimi Feb 27 '22 at 07:27
how I can fix it ? – anoud Feb 27 '22 at 07:29
It happens because '_userService.getUserInfo' returns data that contains name = null. You should find that reason. – M Karimi Feb 27 '22 at 07:36
Yes, and you should fix that in there. – M Karimi Feb 27 '22 at 08:45
I update the question and add the getUserInfo could you take a look and help me please – anoud Feb 27 '22 at 08:47
Are you sure that 'First Name' in 'name: snapshot.get('First Name') ?? '', ' is correct?! Maybe its spelling is wrong. – M Karimi Feb 27 '22 at 08:56

score 0 · Answer 2 · answered Feb 27 '22 at 06:01

0

Error: Null check operator used on a null value

Two way you solve this.

in your model class set variable nullable

final String? profileImageUrl; Use ?.

Or

Set default value if null.

profileImageUrl ?? '' if value is null => ?? ''.

answered Feb 27 '22 at 06:01

A. Sang

381
4
11

Null check operator used on a null value. The relevant error-causing widget was StreamBuilder

2 Answers2