Question 76422 in Flutter Question posted in
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How to solve range error in growable list? – Flutter

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 a screenshot of exception

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]),
          ),
        ]),
      ),
    );
  }
}
Tags:

2

Answers


  1. 0

    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"),
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  2. 0

    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.

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