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.

import 'dart:async';

import 'package:flutter/material.dart';

/// Flutter code sample for [StreamBuilder].

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

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

  static const Duration delay = Duration(seconds: 1);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: StreamBuilderExample(delay: delay),
    );
  }
}

class StreamBuilderExample extends StatefulWidget {
  const StreamBuilderExample({
    required this.delay,
    super.key,
  });

  final Duration delay;

  @override
  State<StreamBuilderExample> createState() => _StreamBuilderExampleState();
}

class _StreamBuilderExampleState extends State<StreamBuilderExample> {
  late final StreamController<int> _controller = StreamController<int>(
    onListen: () async {
      await Future<void>.delayed(widget.delay);

      if (!_controller.isClosed) {
        _controller.add(1);
      }

      await Future<void>.delayed(widget.delay);

      if (!_controller.isClosed) {
        _controller.close();
      }
    },
  );

  Stream<int> get _bids => _controller.stream;

  @override
  void dispose() {
    if (!_controller.isClosed) {
      _controller.close();
    }
    super.dispose();
  }

  @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: BidsStatus(bids: _bids),
      ),
    );
  }
}

class BidsStatus extends StatelessWidget {
  const BidsStatus({
    required this.bids,
    super.key,
  });

  final Stream<int>? bids;

  @override
  Widget build(BuildContext context) {
    return 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: ${snapshot.stackTrace}',
                maxLines: 1,
                overflow: TextOverflow.ellipsis,
              ),
            ),
          ];
        } else {
          switch (snapshot.connectionState) {
            case ConnectionState.none:
              children = const <Widget>[
                Icon(
                  Icons.info,
                  color: Colors.blue,
                  size: 60,
                ),
                Padding(
                  padding: EdgeInsets.only(top: 16),
                  child: Text('Select a lot'),
                ),
              ];
            case ConnectionState.waiting:
              children = const <Widget>[
                SizedBox(
                  width: 60,
                  height: 60,
                  child: CircularProgressIndicator(),
                ),
                Padding(
                  padding: EdgeInsets.only(top: 16),
                  child: Text('Awaiting bids...'),
                ),
              ];
            case ConnectionState.active:
              children = <Widget>[
                const Icon(
                  Icons.check_circle_outline,
                  color: Colors.green,
                  size: 60,
                ),
                Padding(
                  padding: const EdgeInsets.only(top: 16),
                  child: Text('\$${snapshot.data}'),
                ),
              ];
            case ConnectionState.done:
              children = <Widget>[
                const Icon(
                  Icons.info,
                  color: Colors.blue,
                  size: 60,
                ),
                Padding(
                  padding: const EdgeInsets.only(top: 16),
                  child: Text(
                    snapshot.hasData
                        ? '\$${snapshot.data} (closed)'
                        : '(closed)',
                  ),
                ),
              ];
          }
        }

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