How to solve range error in growable list? - flutter

Question

When I am calling getUserById() function everything works fine and the growable string works fine but when I use the same variable inside a text widget then it shows RangeError.
The problem is occuring only when I try to use a growable list of string named as dataAsString inside the build.
Here is the Code with Error. Go to the scaffold where I have commented the line of error
import 'package:Healthwise/helpers/user.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:flutter/material.dart';
import '../helpers/backEnd.dart';
import '../helpers/frontEnd.dart';
class ResultPage extends StatefulWidget {
const ResultPage({Key? key}) : super(key: key);
#override
State<ResultPage> createState() => _ResultPageState();
}
class _ResultPageState extends State<ResultPage> {
// String docId = '';
String objectToString = '';
String e = '';
//This variable is creating the problem...
// I have tried this by using a final instead of var, but nothing worked.
var dataAsString = <String>[];
#override
void initState() {
super.initState();
// getUsers();
getUserById();
}
getUserById() {
final String id = itemName;
userRef.doc(id).get().then((DocumentSnapshot doc) {
// final x = doc.data();
// docId= doc.id;
objectToString = doc.data().toString();
String temp = '';
// print(doc.data());
// print(doc.id);
int i = 1;
// int j = 0;
bool end = false;
//We are just parsing the object into string.
while (objectToString[i] != '}') {
if (objectToString[i - 1] == ' ' && objectToString[i - 2] == ':') {
while (objectToString[i] != ',' && end != true) {
// print(z[i]);
temp += objectToString[i];
if (objectToString[i + 1] != '}') {
i++;
} else {
end = true;
}
}
//Here I add all the strings to list...
// This line works fine.
dataAsString.add(temp);
temp = '';
// j++;
print("The code below this line prints everything perfectly");
print(dataAsString.length);
print(dataAsString[0]);
}
i++;
}
// print(dataAsString[0]);
// print(dataAsString[1]);
// print("+++++++++++");
// print(dataAsString[2]);
// for (var k in dataAsString) {
// print(k);
// }
// print(dataAsString);
// setState(() {});
});
}
// getUsers() {
// userRef.get().then((QuerySnapshot snapshot) {
// snapshot.docs.forEach((DocumentSnapshot doc) {
// print(doc.data());
// print(doc.id);
// print(doc.exists);
// });
// });
// }
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(backgroundColor: primary_color, title: Text("Apple")),
body: Container(
child: Column(children: [
ListTile(
//The problem arises here and the app do not crash if I run the same code with just a //string in place of dataAsString[0]
title: Text(dataAsString[0]),
),
ListTile(
title: Text(dataAsString[1]),
),
ListTile(
title: Text(dataAsString[2]),
),
]),
),
);
}
}

Answer 1

You cant have data on dataAsString because you are using future(.then) on fetching data. You can do value check like
Text( dataAsString.isNotEmpty? dataAsString[0]: "0 is empty"),
Text( dataAsString.length>2? dataAsString[1]: "1 index is empty"),
Text( dataAsString.length>3? dataAsString[2]: "3rd item is empty"),

Answer 2

It's cause your dataAsString ins't ready on first Flutter rendered frame. So, you need to wait for the getUserById finish to access the dataAsString values.
You can use a builder to check if the data is ready in a readable way.
Builder(
builder: (context) {
if (dataAsString.length >= 2) {
return Column(children: [
ListTile(
title: Text(dataAsString[0]),
),
ListTile(
title: Text(dataAsString[1]),
),
ListTile(
title: Text(dataAsString[2]),
),
]);
} else {
return const Center(
child: CircularProgressIndicator(),
);
}
},
),
Warning: it'll work cause you're calling setState when you finish the async task.