Flutter StreamBuilder Shared

main.dart

import 'package:flutter/material.dart';
import 'dart:async';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      routes: {
        '/pageA': (context) => const PageAA(),
        '/pageB': (context) => const PageBB(),
        '/pageC': (context) => const PageCC()
      },
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const PageAA(),
    );
  }
}

class PageAA extends StatefulWidget {
  const PageAA({Key? key}) : super(key: key);

  @override
  State<PageAA> createState() => _PageAAState();
}

class _PageAAState extends State<PageAA> {
  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(builder: (context, constraints) {
      return Container(
        //decoration: BackGroundImage.BackGroundImageBoxDecoration,
        child: Scaffold(
          appBar: AppBar(title: const Text('Page A')),

          //backgroundColor: Colors.transparent,
          body: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                const Center(
                  child: Text(
                    'Start the program in page C',
                    style: TextStyle(
                      color: Colors.black,
                      fontSize: 20,
                    ),
                  ),
                ),
                IconButton(
                  icon: const Icon(Icons.arrow_forward_ios),
                  onPressed: () => Navigator.of(context).pushNamed('/pageB'),
                )
              ],
            ),
          ),
        ),
      );
    });
  }
}

class PageBB extends StatefulWidget {
  const PageBB({Key? key}) : super(key: key);

  @override
  State<PageBB> createState() => _PageBBState();
}

class _PageBBState extends State<PageBB> {
  SeqDepService seqDepService = SeqDepService();

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(builder: (context, constraints) {
      return Container(
        //decoration: BackGroundImage.BackGroundImageBoxDecoration,
        child: Scaffold(
          appBar: AppBar(title: const Text('Page B')),

          //backgroundColor: Colors.transparent,
          body: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                Center(
                  child: StreamBuilder<List<SeqDepEntity>>(
                    stream: seqDepService.activeSeqDepListStream,
                    initialData: seqDepService.activeSeqDepList,
                    builder: ((context, snapshot) {
                      if (snapshot.hasData) {
                        return (Text(
                            'The lenght of last \nSnapshot data is: ${snapshot.data!.length}',
                            style: const TextStyle(
                                color: Colors.black, fontSize: 20)));
                      } else {
                        return Container();
                      }
                    }),
                  ),
                ),
                const SizedBox(height: 50),
                const Center(
                  child: Text(
                    'Enter items on Stream in page C',
                    style: TextStyle(color: Colors.black, fontSize: 15),
                  ),
                ),
                IconButton(
                  icon: const Icon(Icons.arrow_forward_ios),
                  onPressed: () => Navigator.of(context).pushNamed('/pageC'),
                )
              ],
            ),
          ),
        ),
      );
    });
  }
}

class PageCC extends StatefulWidget {
  const PageCC({Key? key}) : super(key: key);

  @override
  State<PageCC> createState() => _PageCCState();
}

class _PageCCState extends State<PageCC> {
  SeqDepService seqDepService = SeqDepService();

  @override
  Widget build(BuildContext context) {
    return LayoutBuilder(builder: (context, constraints) {
      return Container(
        //decoration: BackGroundImage.BackGroundImageBoxDecoration,
        child: Scaffold(
          appBar: AppBar(title: const Text('Page C')),

          //backgroundColor: Colors.transparent,
          body: Padding(
            padding: const EdgeInsets.all(8.0),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: [
                StreamBuilder<List<SeqDepEntity>>(
                    stream: seqDepService.activeSeqDepListStream,
                    initialData: seqDepService.activeSeqDepList,
                    builder: ((context, snapshot) {
                      if (snapshot.hasData) {
                        return (Text(
                            'The lenght of last \nSnapshot data is: ${snapshot.data!.length}',
                            style: const TextStyle(
                                color: Colors.black, fontSize: 20)));
                      } else {
                        return Container();
                      }
                    })),
                Center(
                  child: IconButton(
                    icon: const Icon(
                      Icons.add,
                      size: 30,
                      color: Colors.blue,
                    ),
                    onPressed: () => seqDepService.addActiveSeqDep(
                        SeqDepEntity(id: 'unique', content: 1)),
                  ),
                )
              ],
            ),
          ),
        ),
      );
    });
  }
}

class SeqDepEntity {
  String id;
  int content;

  SeqDepEntity({
    required this.id,
    required this.content,
  });
}

abstract class SeqDepService {
  List<SeqDepEntity> get activeSeqDepList;

  Stream<List<SeqDepEntity>> get activeSeqDepListStream;

  /// Add a single item on stream data. The stream data is a List<SeqDepEntity>
  addActiveSeqDep(SeqDepEntity entity);

  factory SeqDepService() {
    return SeqDepServiceFFmpeg();
  }
}

class SeqDepServiceFFmpeg implements SeqDepService {
  static SeqDepServiceFFmpeg? _instance;
  SeqDepServiceFFmpeg._();

  factory SeqDepServiceFFmpeg() {
    _instance ??= SeqDepServiceFFmpeg._();
    return _instance!;
  }

  final List<SeqDepEntity> _activeListSeqDep = [];
  final StreamController<List<SeqDepEntity>> _controller =
      StreamController<List<SeqDepEntity>>.broadcast();

  @override
  List<SeqDepEntity> get activeSeqDepList => _activeListSeqDep;

  @override
  Stream<List<SeqDepEntity>> get activeSeqDepListStream => _controller.stream;

  @override
  void addActiveSeqDep(SeqDepEntity seqDep) {
    _activeListSeqDep.add(seqDep);
    _addInStream(_activeListSeqDep);
  }

  void _addInStream(List<SeqDepEntity> activeEntities) {
    _controller.sink.add(activeEntities);
  }
}