Flutter API fetch code throws "index out of range"

Question

I wrote a simple webpage widget in Flutter which tries to fetch simple JSON from a public web API but it fails on the very line where it fetches the data. The error message doesn't say anything specific. What am I doing wrong?

import 'dart:convert';
import 'package:flutter/material.dart';
import 'package:http/http.dart' as customhttp;
import '../settings/schemes/color_scheme.dart';

class ContentPage extends StatefulWidget {
  const ContentPage({super.key});

  @override
  State<ContentPage> createState() => _ContentPageState();
}

class _ContentPageState extends State<ContentPage> {
  var _posts = [];

  Future fetchPosts() async {
    try
    {
      String url = "https://jsonplaceholder.typicode.com/posts";
      final customhttp.Response response = await customhttp.get(Uri.parse(url));
      final List<dynamic> jsonData = json.decode(response.body) as List;

      setState(() {
        _posts = jsonData;
      });

      print("Got JSON data.");
      print(_posts[0]);
      
    } catch (err) {}
  }

  @override
  void initState() {
    super.initState();
    fetchPosts();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: schemeBackgroundColor,
      body: Container(
        child: Text("JSON DATA:\n ${_posts[0]}"),
      ),
    );
  }

}

The error I'm getting on line 20:

Answer 1

The error is in the widget.

You are trying to display the first item of the posts even before getting the data.

Text("JSON DATA:\n ${_posts[0]}"),

You should either use FutureBuilder or check if the list is emplty or not before displaying the item.

Example:

Text("JSON DATA:\n ${_posts.isEmpty ? 'No Data' : _posts[0]}"),