android - Flutter:在同一棵树中使用 Multiprovider 和 Consumer 进行依赖注入(inject)

Question

我正在尝试将服务实例(已在同一树级别创建)注入(inject)另一个提供者。但是在访问提供者时沿着树向下，我得到了 ProviderNotFoundException 异常。在下面的代码中，NotificationService 依赖于 AuthService。哪个需要在构造函数中传递。因此，我使用 Consumer 和 Provider.value 注入(inject)它，如文档中所述:https://pub.dev/documentation/provider/latest/provider/Consumer-class.html

伪代码如下:

return MultiProvider(
    providers: [
      Provider<AuthService>(
        create: (ctx) => AuthService(_storage),
        dispose: (ctx, v) => v.dispose(),
      ),
      Consumer<AuthService>(
        builder: (context, v, child) {
          return Provider.value(
              value: Provider<NotificationService>(
                create: (ctx) => NotificationService(v),
                dispose: (ctx, v) => v.dispose(),
              ),
              child: child
          );
        },
      )
    ],
    child: MyApp()
);

树线下的某个地方，当尝试访问 NotificationService 实例时，我得到 ProviderNotFoundException:

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final NotificationService _ns = Provider.of<NotificationService>(context);
  }
}

错误:

I/flutter ( 4614): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 4614): The following ProviderNotFoundException was thrown building MyApp(dirty, dependencies:
I/flutter ( 4614): [_DefaultInheritedProviderScope<AuthService>]):
I/flutter ( 4614): Error: Could not find the correct Provider<NotificationService> above this MyApp Widget
I/flutter ( 4614): 
I/flutter ( 4614): To fix, please:
I/flutter ( 4614): 
I/flutter ( 4614):   * Ensure the Provider<NotificationService> is an ancestor to this MyApp Widget
I/flutter ( 4614):   * Provide types to Provider<NotificationService>
I/flutter ( 4614):   * Provide types to Consumer<NotificationService>
I/flutter ( 4614):   * Provide types to Provider.of<NotificationService>()
I/flutter ( 4614):   * Ensure the correct `context` is being used.
I/flutter ( 4614): 

我不完全理解这一点，我很确定上面的代码有错误。我究竟做错了什么？

Answer 1

您使用 Provider.value 的方式无效。但是你实际上并不需要Consumer+Provider。你可以这样做:

MultiProvider(
  providers: [
    Provider(create: (_) => A()),
    Provider(create: (context) => B(Provider.of<A>(context, listen: false)),
  ],
)