main.dart

import 'dart:async';

import 'package:flutter/material.dart';

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyHomePage(
        title: 'ReorderableListView',
      ),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  MyHomePage({Key key, this.title}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final List<int> data = [];
  StreamController<List<int>> listStream;

  initState() {
    super.initState();
    listStream = StreamController();
  }

  dispose() {
    listStream?.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: [_buildAddButton(), _buildRemoveButton()],
      ),
      body: Center(
        child: StreamBuilder(
          stream: listStream.stream,
          initialData: data,
          builder: (context, snapshot) {
            return ListView(
              children: _buildTiles(),
            );
          },
        ),
      ),
    );
  }

  Widget _buildAddButton() {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 20.0),
      child: IconButton(
        icon: Icon(Icons.add),
        onPressed: () {
          setState(
            () {
              data.add(data.length);
            },
          );
        },
      ),
    );
  }

  Widget _buildRemoveButton() {
    return Padding(
      padding: const EdgeInsets.symmetric(horizontal: 20.0),
      child: IconButton(
        icon: Icon(Icons.remove),
        onPressed: () {
          data.removeLast();
          listStream.add(data);
        },
      ),
    );
  }

  List<Widget> _buildTiles() {
    List<Widget> tiles = data.map((int val) {
      return MyListTile(
        key: ValueKey(val),
        data: val,
        title: "tile $val",
      );
    }).toList();
    return tiles;
  }
}

class MyListTile extends StatefulWidget {
  final int data;
  final String title;

  MyListTile({this.data, this.title, Key key}) : super(key: key);

  @override
  _MyListTileState createState() => _MyListTileState();
}

class _MyListTileState extends State<MyListTile> {
  Stream<int> _msStream;
  int _curMs;

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

    print("init: ${widget.title}");
    _curMs = 0;
    _msStream = Stream.periodic(const Duration(milliseconds: 100), (ms) => ms);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: const EdgeInsets.symmetric(vertical: 20.0, horizontal: 30.0),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.spaceBetween,
        children: [
          Text("${widget.title}"),
          StreamBuilder<int>(
            stream: _msStream,
            initialData: _curMs,
            builder: (_, AsyncSnapshot<int> snapshot) {
              if (!snapshot.hasData)
                return Center(child: CircularProgressIndicator());

              String ms = "${snapshot.data} ms";
              return Text(ms);
            },
          )
        ],
      ),
    );
  }

  void dispose() {
    print("dispose: ${widget.title}");
    super.dispose();
  }
}