dependencies:
  http: ^0.13.5

flutter pub get

import 'package:http/http.dart' as http;
import 'dart:convert';

void fetchData() async {
  final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts/1'));
  if (response.statusCode == 200) {
    final data = jsonDecode(response.body);
    print(data['title']);
  }
}

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: HomePage());
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  String title = "โหลดข้อมูล...";

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

  void fetchTitle() async {
    final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts/1'));
    if (response.statusCode == 200) {
      final data = jsonDecode(response.body);
      setState(() {
        title = data['title'];
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text("ข้อมูลจาก API")),
      body: Center(child: Text(title)),
    );
  }
}