文档

dependencies:
provider:

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

class Counter with ChangeNotifier {
Counter() {
printf('init');
}
int _n = 0;
int get n => _n;
set n(v) {
_n = v;
notifyListeners();
}
}

void main() {
var app = MultiProvider( providers: [ ChangeNotifierProvider(create: () => Counter()),

  // var counter = Counter();
  // ChangeNotifierProvider.value(value: counter),
],
child: MyApp(),

);
runApp(_app);
}

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: HomePage(),
);
}
}

class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}

class _HomePageState extends State {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Home Page'),
),
body: Column(
children: [
Center(
child: Text('home page ${context.watch().n}'),
),
W1(),
W2(),
],
),
floatingActionButton: FloatingActionButton(
onPressed: () {
context.read().n++;
},
),
);
}
}

class W1 extends StatefulWidget {
@override
_W1State createState() => _W1State();
}

class _W1State extends State {
@override
Widget build(BuildContext context) {
return Container(
width: 100,
height: 100,
child: Text(context.watch().n.toString()),
);
}
}

class W2 extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Container(
width: 100,
height: 100,
child: Text(context.watch().n.toString()),
);
}
}