防止“尝试使用具有可听/流子类型的提供程序”颤动错误

Question

我想在我的颤振项目中使用提供程序包（4.0），但我收到“试图使用具有可听/流子类型的提供程序”错误/警告。

我的星座：

我有一个Api()包含用于 firebase-cloudstorage 的基本 CRUD 功能的类。

我有一个EventService()-class，它使用Api()带有具体参数的-class。

对于我的观点，我有一个EventOverviewModel使用 EventService的 ViewModel 类。

我的提供程序配置如下所示：

List<SingleChildWidget> providers = [
  ...independentServices,
  ...dependentServices,
  ...uiConsumableProviders,
];

// Services die unabhängig von anderen sind
List<SingleChildWidget> independentServices = [
  Provider<EventService>(create: (_) => EventService(api: Api('events')))
];

// Services die von anderen Services abhängig sind
List<SingleChildWidget> dependentServices = [
  ProxyProvider<EventService, EventOverviewModel>(
    update: (_, srvc, __) => EventOverviewModel(eventService: srvc),
  )
];

List<SingleChildWidget> uiConsumableProviders = [];

一切似乎都在应用程序中工作，但无论如何我都得到了“尝试使用具有可听/流子类型的提供程序”。

我应该如何更改我的代码以不再收到此错误消息？

Running Gradle task 'assembleDebug'...
I/flutter (16553): ??? EXCEPTION CAUGHT BY WIDGETS LIBRARY ????????????????????????????????????????????????????????????
I/flutter (16553): The following assertion was thrown building NumericProxyProvider<EventService, Void, Void, Void,
I/flutter (16553): Void, Void, EventOverviewModel>(dirty, dependencies: [InheritedProvider<EventService>], state:
I/flutter (16553): _ProxyProviderState<EventOverviewModel>#8d38d):
I/flutter (16553): Tried to use Provider with a subtype of Listenable/Stream (EventOverviewModel).
I/flutter (16553): 
I/flutter (16553): This is likely a mistake, as Provider will not automatically update dependents
I/flutter (16553): when EventOverviewModel is updated. Instead, consider changing Provider for more specific
I/flutter (16553): implementation that handles the update mechanism, such as:
I/flutter (16553): 
I/flutter (16553): - ListenableProvider
I/flutter (16553): - ChangeNotifierProvider
I/flutter (16553): - ValueListenableProvider
I/flutter (16553): - StreamProvider
I/flutter (16553): 
I/flutter (16553): Alternatively, if you are making your own provider, consider using InheritedProvider.
I/flutter (16553): 
I/flutter (16553): If you think that this is not an error, you can disable this check by setting
I/flutter (16553): Provider.debugCheckInvalidValueType to `null` in your main file:
I/flutter (16553): 
I/flutter (16553): ```
I/flutter (16553): void main() {
I/flutter (16553):   Provider.debugCheckInvalidValueType = null;
I/flutter (16553): 
I/flutter (16553):   runApp(MyApp());
I/flutter (16553): }
I/flutter (16553): ```
I/flutter (16553): 
I/flutter (16553): 
I/flutter (16553): The relevant error-causing widget was:
I/flutter (16553):   NumericProxyProvider<EventService, Void, Void, Void, Void, Void, EventOverviewModel>
I/flutter (16553):   file:///E:/Dev/flutter/.pub-cache/hosted/pub.dartlang.org/provider-3.2.0/lib/src/proxy_provider.dart:232:12
I/flutter (16553): 
I/flutter (16553): When the exception was thrown, this was the stack:
I/flutter (16553): #0      Provider.debugCheckInvalidValueType.<anonymous closure>.<anonymous ...

Answer 1

尝试改变

List<SingleChildWidget> independentServices = [
  Provider<EventService>(create: (_) => EventService(api: Api('events')))
];

到：

List<SingleChildWidget> independentServices = [
  ListenableProvider<EventService>(create: (_) => EventService(api: Api('events')))
];

和

List<SingleChildWidget> dependentServices = [
  ProxyProvider<EventService, EventOverviewModel>(
    update: (_, srvc, __) => EventOverviewModel(eventService: srvc),
  )
];

到：

List<SingleChildWidget> dependentServices = [
  ListenableProxyProvider<EventService, EventOverviewModel>(
    update: (_, srvc, __) => EventOverviewModel(eventService: srvc),
  )
];

我猜 EventService 或 EventOverviewModel 扩展或混合，ChangeNotifier并且在您的代码中的某处您正在侦听Provider<EventService>and值的ProxyProvider<EventOverviewModel>更改，但除非您的提供程序是“可听”的，否则这些更改将永远不会被广播/接收。

因此，如果您的模型扩展/混合ChangeNotifier，并且它们正在调用notifyListeners()，则这些模型的提供者至少需要“可听”。

ListenableProvider
ListenableProxyProvider

...或者更好的是，您的模型可以使用 ChangeNotifier 版本：

ChangeNotifierProvider
ChangeNotifierProxyProvider

...当这些对象不再使用时，它可以方便地处理/分离任何侦听器（释放资源）。

Answer 2

使用 Provider 包时，存在一些问题。默认情况下，在 中声明的所有提供程序实例providers:[]都是不可侦听的。因此，在这种情况下，您需要使用ChangeNotifierProvider(create: (_) =>Model())orListenableProvider(create: (_) =>Model())或来初始化它们StreamProvider(create: (_) =>Model())

\n

    List<SingleChildWidget> independentServices = [\n  ChangeNotifierProvider<EventService>(create: (_) => EventService(api: Api('events')))\n];\n\n// Services die von anderen Services abh\xc3\xa4ngig sind\nList<SingleChildWidget> dependentServices = [\n  ChangeNotifierProxyProvider<EventService, EventOverviewModel>(\n    update: (_, srvc, __) => EventOverviewModel(eventService: srvc),\n  )\n];\n

\n