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.

// Template: dev/snippets/config/templates/stateful_widget_material.tmpl
//
// Comment lines marked with "▼▼▼" and "▲▲▲" are used for authoring
// of samples, and may be ignored if you are just exploring the sample.

// Flutter code sample for StreamBuilder
//
//***************************************************************************
//* ▼▼▼▼▼▼▼▼ description ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

// This sample shows a [StreamBuilder] that listens to a Stream that emits bids
// for an auction. Every time the StreamBuilder receives a bid from the Stream,
// it will display the price of the bid below an icon. If the Stream emits an
// error, the error is displayed below an error icon. When the Stream finishes
// emitting bids, the final price is displayed.

//* ▲▲▲▲▲▲▲▲ description ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//***************************************************************************

import 'package:flutter/material.dart';

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

/// This is the main application widget.
class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

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

/// This is the stateful widget that the main application instantiates.
class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

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

/// This is the private State class that goes with MyStatefulWidget.
class _MyStatefulWidgetState extends State<MyStatefulWidget> {
//********************************************************************
//* ▼▼▼▼▼▼▼▼ code ▼▼▼▼▼▼▼▼ (do not modify or remove section marker)

  final Stream<int> _bids = (() async* {
    await Future<void>.delayed(const Duration(seconds: 1));
    yield 1;
    await Future<void>.delayed(const Duration(seconds: 1));
  })();

  @override
  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: Theme.of(context).textTheme.headline2!,
      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: ${snapshot.stackTrace}'),
                ),
              ];
            } else {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  children = const <Widget>[
                    Icon(
                      Icons.info,
                      color: Colors.blue,
                      size: 60,
                    ),
                    Padding(
                      padding: EdgeInsets.only(top: 16),
                      child: Text('Select a lot'),
                    )
                  ];
                  break;
                case ConnectionState.waiting:
                  children = const <Widget>[
                    SizedBox(
                      child: CircularProgressIndicator(),
                      width: 60,
                      height: 60,
                    ),
                    Padding(
                      padding: EdgeInsets.only(top: 16),
                      child: Text('Awaiting bids...'),
                    )
                  ];
                  break;
                case ConnectionState.active:
                  children = <Widget>[
                    const Icon(
                      Icons.check_circle_outline,
                      color: Colors.green,
                      size: 60,
                    ),
                    Padding(
                      padding: const EdgeInsets.only(top: 16),
                      child: Text('\$${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,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: children,
            );
          },
        ),
      ),
    );
  }

//* ▲▲▲▲▲▲▲▲ code ▲▲▲▲▲▲▲▲ (do not modify or remove section marker)
//********************************************************************

}