database - 如何在 Flutter 中的不同应用页面之间正确共享对象

Question

我是 Flutter 的新手。我已经实现了一个任意类，它有一些状态，需要在 Flutter 的不同页面之间共享。我目前正在做的是我定义了一个 sqflite数据库助手和每个页面加载该对象表单数据库，在转到其他页面之前，它再次将其保存到数据库并导航到其他页面。但是，它增加了许多复杂性和错误。

另一种可能的解决方案是将其添加到 myApp()在 main() 中调用的类功能。但是，由于其他页面不继承 myApp() ，他们无权访问 global_object .

class MyApp extends StatelessWidget{

// I need gloabl_object accessible in different pages
//--------------------------------------------------- 
MyObject global_object; 
//---------------------------------------------------

  @override
  Widget build(BuildContext context){
    return MaterialApp(
      title: 'App title',
      debugShowCheckedModeBanner: false,
      theme: new ThemeData(
        // App theme
      ),
      //home: Homepage(),
      routes: { // Defining routs
        // DIFFERENT PAGES THAT NEEDS TO HAVE ACCESS TO global_object
      },
    );
}

Answer 1

方法一 : 使用包 get_it https://pub.dev/packages/get_it
简单直接Service Locator这允许将接口(interface)与具体实现分离，并从应用程序中的任何地方访问具体实现。
示例 https://github.com/fluttercommunity/get_it/tree/master/example/lib

GetIt sl = GetIt.instance;

void main() {

  sl.registerSingleton<AppModel>(AppModelImplementation());

  runApp(MyApp());
}

注册后，您可以随处访问

var myAppModel = sl.get<AppModel>();

方法二 : 使用包提供者 https://pub.dev/packages/provider
完整示例 https://github.com/flutter/samples/tree/master/provider_shopper

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Using MultiProvider is convenient when providing multiple objects.
    return MultiProvider(
      providers: [
        // In this sample app, CatalogModel never changes, so a simple Provider
        // is sufficient.
        Provider(create: (context) => CatalogModel()),
        // CartModel is implemented as a ChangeNotifier, which calls for the use
        // of ChangeNotifierProvider. Moreover, CartModel depends
        // on CatalogModel, so a ProxyProvider is needed.
        ChangeNotifierProxyProvider<CatalogModel, CartModel>(
          create: (context) => CartModel.empty(),
          update: (context, catalog, previousCart) =>
              CartModel(catalog, previousCart),
        ),
      ],
      child: MaterialApp(
        title: 'Provider Demo',
        theme: appTheme,
        initialRoute: '/',
        routes: {
          '/': (context) => MyCatalog(),
          '/cart': (context) => MyCart(),
        },
      ),
    );
  }
}

访问 Provider.of<CartModel>(context);

class _CartList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var itemNameStyle = Theme.of(context).textTheme.title;
    var cart = Provider.of<CartModel>(context);

    return ListView.builder(
      itemCount: cart.items.length,

或与 Consumer<CartModel>

class _CartTotal extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    var hugeStyle = Theme.of(context).textTheme.display4.copyWith(fontSize: 48);

    return SizedBox(
      height: 200,
      child: Center(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Consumer<CartModel>(
                builder: (context, cart, child) =>
                    Text('\$${cart.totalPrice}', style: hugeStyle)),