ValueListenerProvider example

valuelistenerprovider_example.dart

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

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

class CountDown extends ValueNotifier<int> {
  CountDown(int downFrom) : super(downFrom) {
    scheduleDecrement();
  }

  void scheduleDecrement() {
    Future.delayed(Duration(seconds: 1), () {
      if (--value > 0) scheduleDecrement();
    });
  }
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    const appTitle = 'ValueListenerProvider Demo';
    return MaterialApp(
        title: appTitle,
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: ValueListenableProvider<int>(
          builder: (context) => CountDown(10),
          child: Scaffold(
            appBar: AppBar(
              title: Text(appTitle),
            ),
            body: Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Consumer<int>(
                    builder: (context, count, child) {
                      if (count > 0) {
                        return Text("T minus $count seconds");
                      }
                      return Text("Blast off!");
                    },
                  ),
                ],
              ),
            ),
          ),
        ));
  }
}