DefaultFutureBuilder.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: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Future<List<MyData>> fetchMyDataList() async {
    await Future.delayed(Duration(seconds: 1));
    return [
      MyData('a'),
      MyData('b'),
      MyData('c'),
    ];
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Builder(
          builder: (_) {
            return DefaultFutureBuilder<List<MyData>>(
              future: fetchMyDataList(),
              builder: (context, List<MyData> list) => ListView.builder(
                itemCount: list.length,
                itemBuilder: (_, index) => Text(list[index].text),
              ),
            );
          }
        )
      ),
    );
  }
}

class MyData {
  MyData(this.text);
  final String text;
}

class DefaultFutureBuilder<T> extends StatefulWidget {
  final Future<T> future;
  final Widget Function(BuildContext, T data) builder;
  final Widget Function(BuildContext) errorBuilder;

  DefaultFutureBuilder({
    @required this.future,
    @required this.builder,
    this.errorBuilder
  });

  @override
  _DefaultFutureBuilderState createState() => _DefaultFutureBuilderState<T>();
}

class _DefaultFutureBuilderState<T> extends State<DefaultFutureBuilder<T>> {
  @override
  Widget build(BuildContext context) {
    var errorBuilder = widget.errorBuilder ?? (_) => Container();

    return FutureBuilder<T>(
      future: widget.future,
      builder: (BuildContext context, AsyncSnapshot<T> snapshot) {
        var indicator = CircularProgressIndicator();

        if (snapshot.hasData)
          return widget.builder(context, snapshot.data);
        else if (snapshot.hasError)
          return errorBuilder(context);

        return indicator;
      },
    );
  }
}