Simplest Provider with ChangeNotifier Example

main.dart

import 'dart:async';

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

void main() {
  runApp(ChangeNotifierProvider(
    create: (_) => Counter(),
    child: MyApp(),
  ));
}

class Counter extends ChangeNotifier {
  Counter() {
    Timer.periodic(Duration(seconds: 1), (timer) { 
      _count++;
      notifyListeners();
    });
  }
  int _count = 42;
  int get count => _count;
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: RichText(
        text: TextSpan(text: context.watch<Counter>().count.toString()),
        textDirection: TextDirection.ltr,
      ),
    );
  }
}