LateInitializationError: Field not initialized Error in Flutter - flutter

Question

Can anyone help me with this problem?
I have the requester class, with the username attribute, as shown in the example below:
class Requester {
late String username;
}
I also have the getInformation() method, which is called in the "click" event, as shown in the example below:
getInformation() async {
Requester requester = Requester();
RequesterEndpoints endpoint = RequesterEndpoints();
final String token = "tokenExemplo";
final uri = Uri.parse(endpoint.getInformation);
final headers = {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*',
'Accept': 'application/json',
'Authorization': 'Bearer ${token}'
};
Response response = await get(uri, headers: headers);
dynamic responseBody = jsonDecode(response.body);
dynamic requesterBody = responseBody['requester'];
requester.username = requesterBody['username'];
}
The method, in the last line, changes, or should change, the value of the username attribute of the requester class. The requesterBody['username'] is a String type value, coming from an API. If I make one:
print(requesterBody['username'])
The username coming from the API will be displayed. That is, the value exists.
If I do a print on requester.username, right after requester.username = requesterBody['username'];, I can see that the username attribute was changed successfully.
I want to use this requester.username value in a view. I'm doing it this way:
import 'package:flutter/material.dart';
import 'package:mobile/models/requester.dart';
class HomeRequesterScreen extends StatefulWidget {
const HomeRequesterScreen({Key? key}) : super(key: key);
#override
State<HomeRequesterScreen> createState() => _HomeRequesterScreenState();
}
class _HomeRequesterScreenState extends State<HomeRequesterScreen> {
Requester requester = Requester();
#override
Widget build(BuildContext context) {
return Container(
child: Text(requester.username);
);
}
}
It is important to mention that the view is only called after the username attribute has been changed, in the getInformation() method.
But when I assign requester.username to Text, I get this error:
LateError (LateInitializationError: Field 'username' has not been initialized.)
In a direct way, I want to use the attribute value of a class in a view.
Does anyone know how to resolve this?

Answer 1

From the code that you shared:
in _HomeRequesterScreenState you just create a new instance of Requester and never assign any value to it. It does not contain anything.
Your getInformation() method is void, you create a variable there and never pass it anywhere even though you called the method.
In DTO classes, like your model, it's not a good practice to use late variables, if not for a reason. In your case, absolutely no need to.
So first, get rid of late, this way it would be easier for you understand if you are actually placing any data where you think it should be.
class Requester {
final String username;
Requester({required this.username});
}
Then make your method return your model.
Future<Requester> getInformation() async {
RequesterEndpoints endpoint = RequesterEndpoints();
final String token = "tokenExemplo";
final uri = Uri.parse(endpoint.getInformation);
final headers = {
'Content-Type': 'application/json',
'Access-Control-Allow-Origin': '*',
'Accept': 'application/json',
'Authorization': 'Bearer ${token}'
};
Response response = await get(uri, headers: headers);
dynamic responseBody = jsonDecode(response.body);
dynamic requesterBody = responseBody['requester'];
return Requester(username: requesterBody['username']);
}
Then explicitly create the instance in your business logic / state management level and pass it to UI.
Since I only have your UI code, let's assume we just do it there. Not to forget that while your API call is in progress, you don't have username to show, so you need to show something else instead and call setState once loaded.
import 'package:flutter/material.dart';
import 'package:mobile/models/requester.dart';
class HomeRequesterScreen extends StatefulWidget {
const HomeRequesterScreen({Key? key}) : super(key: key);
#override
State<HomeRequesterScreen> createState() => _HomeRequesterScreenState();
}
class _HomeRequesterScreenState extends State<HomeRequesterScreen> {
Requester? requester;
#override
void initState() {
super.initState();
loadRequester();
}
Future<void> loadRequester() async {
requester = await getInformation();
setState(() {});
}
#override
Widget build(BuildContext context) {
return Container(
child: requester != null ? Text(requester!.username) : CircularProgressIndicator();
);
}
}