Straightforward

mobx_provider.dart

import 'package:flutter/material.dart' hide Action;
import 'package:flutter_mobx/flutter_mobx.dart';
import 'package:mobx/mobx.dart';
import 'package:provider/provider.dart';

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

class Counter {
  Action increment;

  Counter() {
    increment = Action(_increment);
  }

  final _value = Observable(0);
  int get value => _value.value;
  void set value(int newValue) => _value.value = newValue;

  void _increment() {
    value++;
  }

  static Counter of(BuildContext context) => Provider.of<Counter>(context);
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Provider<Counter>(
      create: (_) => Counter(),
      child: MaterialApp(
        title: 'Flutter Demo',
        theme: ThemeData(
          primarySwatch: Colors.blue,
        ),
        home: MyHomePage(title: 'Flutter Demo Home Page'),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final String title;

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Observer(
              builder: (context) => Text(
                Counter.of(context).value.toString(),
                style: Theme.of(context).textTheme.display1,
              ),
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: Counter.of(context).increment,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}