pika3113
Reputation: 65
Null check operator used on a null value (error)
This is the code:
// ignore_for_file: prefer_const_constructors, prefer_const_literals_to_create_immutables
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';
import 'package:google_nav_bar/google_nav_bar.dart';
import 'package:projectciplified/screens/read%20data/get_user_name.dart';
class HomePage extends StatefulWidget {
const HomePage({Key? key}) : super(key: key);
@override
State<HomePage> createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
final user = FirebaseAuth.instance.currentUser!;
//document ids
List<String> docIDs = [];
// method to get document ids
Future getDocID() async {
await FirebaseFirestore.instance.collection('users').get().then(
(snapshot) => snapshot.docs.forEach(
(document) {
print(document.reference);
docIDs.add(document.reference.id);
},
),
);
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(
user.email!,
style: TextStyle(fontSize: 16),
),
actions: [
GestureDetector(
onTap: () {
FirebaseAuth.instance.signOut();
},
child: Icon(Icons.logout)),
],
),
bottomNavigationBar: Container(
color: Colors.black,
child: Padding(
padding: const EdgeInsets.symmetric(
horizontal: 15,
vertical: 20.0,
),
child: GNav(
backgroundColor: Colors.black,
color: Colors.white,
activeColor: Colors.white,
tabBackgroundColor: Colors.blue,
padding: EdgeInsets.all(10),
gap: 2,
onTabChange: (index) {},
tabs: [
GButton(
icon: Icons.home,
text: 'Home',
),
GButton(
icon: Icons.favorite_border,
text: 'likes',
),
GButton(
icon: Icons.search,
text: 'search',
),
GButton(
icon: Icons.settings,
text: 'settings',
),
],
),
),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Expanded(
child: FutureBuilder(
future: getDocID(),
builder: (context, snapshot) {
return ListView.builder(
itemCount: docIDs.length,
itemBuilder: (context, index) {
return Padding(
padding: const EdgeInsets.all(8.0),
child: ListTile(
tileColor: Colors.grey[200],
title: GetUserName(documentID: docIDs[index]),
),
);
},
);
},
)),
],
),
),
);
}
}
I'm trying to get the user info with FirebaseAuth.instance.currentUser! but it's giving said error. With FirebaseAuth.instance.currentUser (without the !) The code works but why?
Can someone explain the null error? I'm not sure why this code doesn't work as it worked around 5 hours ago. How do I fix it? Thanks for your help.
Upvotes: 0
Views: 193
Answers (1)
Md. Yeasin Sheikh
Reputation: 63594
There are few states FutureBuilder provides, like connection state, error state and data or empty state. While you calling future it needs some time to fetch data, means first state is loading state and data is not ready yet. That's why it says null error because we don't have any data.
Do like
FutureBuilder(
future: getDocID(),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting) {
return Center(child: Text('Please wait its loading...'));
} else if (snapshot.hasError) {
return Center(child: Text('Error: ${snapshot.error}'));
} else if (snapshot.hasData) {
return ListView(...);
}
else return Text("dont have any data")
},
Find more about FutureBuilder on flutter.dev.
Upvotes: 1
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