Flutter：在同一棵树中使用 Multiprovider 和 Consumer 进行依赖注入

Question

我正在尝试将服务实例（已在同一树级别中创建）注入另一个提供程序。 但是在访问提供程序时，我得到了ProviderNotFoundException异常。 在下面的代码中NotificationService依赖于AuthService 。 这需要在构造函数中传递。 因此，我使用文档中提到的Consumer和Provider.value注入它： https : //pub.dev/documentation/provider/latest/provider/Consumer-class.html

这是伪代码：

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()
);

在树线的某处，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中存在错误。 我究竟做错了什么？

Answer 1

您使用Provider.value方式无效。 但是您实际上并不需要Consumer + Provider 。 你可以做：

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