[flutter] FutureBuilder

1)

2) home_screen.dart

import 'dart:math';

import 'package:flutter/material.dart';

class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    final textStyle = TextStyle(
      fontSize: 16.0,
    );
    return Scaffold(
      body: Padding(
        padding: const EdgeInsets.all(8.0),
        child: FutureBuilder(
          future: getNumber(),
          builder: (context, snapshot) {
            if(snapshot.hasData){
              // 데이터가 있을 때 위젯 렌더링
            }

            if(snapshot.hasError){
              // 에러가 났을 때 위젯 렌더링
            }

            // 로딩중일 때 위젯 렌더링
            
            return Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.stretch,
              children: [
                Text(
                  'FutureBuilder',
                  style: textStyle.copyWith(
                      fontWeight: FontWeight.w700, fontSize: 20.0),
                ),
                Text(
                  'ConState : ${snapshot.connectionState}',
                  style: textStyle,
                ),
                Text(
                  'Data : ${snapshot.data}',
                  style: textStyle,
                ),
                Text(
                  'Error : ${snapshot.error}',
                  style: textStyle,
                ),
                ElevatedButton(
                  onPressed: () {
                    setState(() {});
                  },
                  child: Text(
                    'SetState',
                  ),
                ),
              ],
            );
          },
        ),
      ),
    );
  }

  Future<int> getNumber() async {
    await Future.delayed(Duration(seconds: 3));
    final random = Random();

    return random.nextInt(100);
  }
}

3)

FutureBuilder를 사용하면 setState가 되는 동안에 데이터는 그대로 이기 때문에 캐싱에 매우 유리하다.