Future Builder Example

readme.md

Future Builder Example

Created with <3 with dartpad.dev.

main.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const FutureBuilderExample(),
    );
  }
}

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

  @override
  State<FutureBuilderExample> createState() => _FutureBuilderExampleState();
}

class _FutureBuilderExampleState extends State<FutureBuilderExample> {
  Future<bool>? _future;
  @override
  void initState() {
    super.initState();
    _future = myFuture();
  }

  Future<bool> myFuture() async {
    await Future.delayed(const Duration(
        seconds: 2)); //Aguarda 2 segundos para prosseguir com o resto do código
    var currentSeccond = DateTime.now().second; //Salva o segundo da hora atual
    debugPrint(
        'currentSeccond = $currentSeccond'); //Printa o número no DEBUG CONSOLE
    return currentSeccond
        .isEven; //Retorna TRUE quando o número for par, FALSE quando ímpar
  }

  @override
  Widget build(BuildContext context) {
    debugPrint('setState executado');
    return Material(
      child: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            FutureBuilder<bool>(
              future: _future,
              builder: (context, snapshot) {
                if (snapshot.connectionState == ConnectionState.waiting) {
                  return Container(
                    width: 100,
                    height: 100,                 
                    color: Colors.transparent,
                    child: const Center(child: CircularProgressIndicator()),
                  );
                } else {
                  final isEven = snapshot.data ?? false;
                  return Container(
                    width: 100,
                    height: 100,
                    color: isEven ? Colors.green : Colors.red,
                    child: Center(child: Text(isEven ? "Impar" : "Par")),
                  );
                }
              },
            ),
            const SizedBox(height: 10),
            ElevatedButton(
              child: const Text('setState'),
              onPressed: () {
                setState(
                    () {}); //Apenas um setState para mostrar que o método não será chamado novamente.
              },
            ),
            const SizedBox(height: 10),
            ElevatedButton(
              child: const Text('Reload function'),
              onPressed: () {
                setState(() {
                  _future = myFuture(); //Recarrega a função
                });
              },
            ),
          ],
        ),
      ),
    );
  }
}