flutter状态管理provider的简单使用

这里我们使用的是官方提供的provider
链接地址：https://pub.flutter-io.cn/packages/provider

接下来使用一个简单的例子，实现两个组件之间值的同时改变

provider类的代码

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

class Counter with ChangeNotifier {
    
    
  int _count = 0;

  int get count => _count;
  intCount() {
    
    
    _count++;
    notifyListeners();
  }
}

在根组件外面嵌套一个组件MultiProvider

import 'package:flutter/material.dart';

import 'package:provider/provider.dart';

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

class MyApp extends StatefulWidget {
    
    
  MyApp({
    
    Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
    
    
  @override
  Widget build(BuildContext context) {
    
    
    return MultiProvider(
      providers: [
        ChangeNotifierProvider(create: (_) => Counter()),
        //如果有多个provider则在这里按上面的方法再写
      ],
      child: ......,
    );
  }
}

·两个组件里面的代码：
Cart.dart

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

class CartPage extends StatefulWidget {
    
    
  CartPage({
    
    Key? key}) : super(key: key);

  @override
  State<CartPage> createState() => _CartPageState();
}

class _CartPageState extends State<CartPage> {
    
    
  @override
  Widget build(BuildContext context) {
    
    
    var counterProvider = Provider.of<Counter>(context);
    return Scaffold(
      floatingActionButton: FloatingActionButton(
        onPressed: () {
    
    
          counterProvider.intCount();
        },
        child: Icon(Icons.add),
      ),
      body: Center(
      child: Text("${counterProvider.count}"),
    ),
    );
  }
}

USer.dart

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

class UserPage extends StatefulWidget {
    
    
  UserPage({
    
    Key? key}) : super(key: key);

  @override
  State<UserPage> createState() => _UserPageState();
}

class _UserPageState extends State<UserPage> {
    
    
  @override
  Widget build(BuildContext context) {
    
    
    var counterProvider = Provider.of<Counter>(context);
    return Center(
      child: Text("${counterProvider.count}"),
    );
  }
}

当点击加号时，购物车页面数字递增时，我的页面内数字也会跟着增大。平时我们要页面发生改变时会使用setState来让build方法重新执行让界面重新加载，这里我们不用setState，provider中notifyListeners();方法的调用也会让界面重新加载，两个页面都是从provider中获取值渲染在页面上。