test.dart

import 'dart:async';

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

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

  ///
  ///
  ///
  @override
  _ExampleScreenState createState() => _ExampleScreenState();
}

///
///
///
class _ExampleScreenState extends State<ExampleScreen> {
  final StreamController<int?> _appBarCountStreamController =
      StreamController<int?>();

  final StreamController<List<String>> theStream =
      StreamController<List<String>>();

  @override
  void initState() {
    super.initState();
    _simulatingLoading();
  }

  ///
  ///
  ///
  Future<void> _simulatingLoading() async {
    await Future<void>.delayed(Duration(seconds: 5));
    List<String> strings = <String>['A', 'B', 'C', 'D', 'E', 'F'];
    theStream.add(strings);
  }

  ///
  ///
  ///
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: StreamBuilder<int?>(
          stream: _appBarCountStreamController.stream,
          builder: (BuildContext context, AsyncSnapshot<int?> snapshot) {
            if (snapshot.data == null) {
              return Wrap(
                children: <Widget>[
                  Text('Loading'),
                  CupertinoActivityIndicator()
                ],
              );
            } else {
              return Text('Total :${snapshot.data}');
            }
          },
        ),
      ),
      body: StreamBuilder<List<String>>(
        stream: theStream.stream,
        builder: (BuildContext context, AsyncSnapshot<List<String>> snapshot) {
          if (snapshot.hasData) {
            _appBarCountStreamController.add(snapshot.data!.length);
            return ListView.builder(
              itemCount: snapshot.requireData.length,
              itemBuilder: (BuildContext context, int index) =>
                  Text(snapshot.data![index]),
            );
          }
          return Wrap(
            children: <Widget>[Text('Loading'), CupertinoActivityIndicator()],
          );
        },
      ),
    );
  }

  ///
  ///
  ///
  @override
  void dispose() {
    _appBarCountStreamController.close();
    theStream.close();
    super.dispose();
  }
}