flutter/examples/api/lib/widgets/async/stream_builder.0.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Flutter code sample for StreamBuilder

import 'dart:async';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}

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

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  final Stream<int> _bids = (() {
    late final StreamController<int> controller;
    controller = StreamController<int>(
      onListen: () async {
        await Future<void>.delayed(const Duration(seconds: 1));
        controller.add(1);
        await Future<void>.delayed(const Duration(seconds: 1));
        await controller.close();
      },
    );
    return controller.stream;
  })();

  @override
  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: Theme.of(context).textTheme.displayMedium!,
      textAlign: TextAlign.center,
      child: Container(
        alignment: FractionalOffset.center,
        color: Colors.white,
        child: StreamBuilder<int>(
          stream: _bids,
          builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
            List<Widget> children;
            if (snapshot.hasError) {
              children = <Widget>[
                const Icon(
                  Icons.error_outline,
                  color: Colors.red,
                  size: 60,
                ),
                Padding(
                  padding: const EdgeInsets.only(top: 16),
                  child: Text('Error: ${snapshot.error}'),
                ),
                Padding(
                  padding: const EdgeInsets.only(top: 8),
                  child: Text('Stack trace: ${snapshot.stackTrace}'),
                ),
              ];
            } else {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  children = const <Widget>[
                    Icon(
                      Icons.info,
                      color: Colors.blue,
                      size: 60,
                    ),
                    Padding(
                      padding: EdgeInsets.only(top: 16),
                      child: Text('Select a lot'),
                    ),
                  ];
                  break;
                case ConnectionState.waiting:
                  children = const <Widget>[
                    SizedBox(
                      width: 60,
                      height: 60,
                      child: CircularProgressIndicator(),
                    ),
                    Padding(
                      padding: EdgeInsets.only(top: 16),
                      child: Text('Awaiting bids...'),
                    ),
                  ];
                  break;
                case ConnectionState.active:
                  children = <Widget>[
                    const Icon(
                      Icons.check_circle_outline,
                      color: Colors.green,
                      size: 60,
                    ),
                    Padding(
                      padding: const EdgeInsets.only(top: 16),
                      child: Text('\$${snapshot.data}'),
                    ),
                  ];
                  break;
                case ConnectionState.done:
                  children = <Widget>[
                    const Icon(
                      Icons.info,
                      color: Colors.blue,
                      size: 60,
                    ),
                    Padding(
                      padding: const EdgeInsets.only(top: 16),
                      child: Text('\$${snapshot.data} (closed)'),
                    ),
                  ];
                  break;
              }
            }

            return Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: children,
            );
          },
        ),
      ),
    );
  }
}