Question

我正在尝试从F＃订阅/取消订阅C＃制造的（在RabbitMQ客户端库中）：

AsyncEventingBasicConsumer.cs

public event AsyncEventHandler<BasicDeliverEventArgs> Received;

AsyncEventHandler.cs

public delegate Task AsyncEventHandler<in TEvent>(object sender, TEvent @event) where TEvent : EventArgs;

我设法通过以下方式订阅了该活动：

let subscribeAsync (channel: IModel) exchange callback =
    let consumer = AsyncEventingBasicConsumer(channel)
    consumer.add_Received(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
    // ...

话虽这么说，我想知道为什么下面的代码无法编译：

let subscribeAsync (channel: IModel) exchange callback =
    let consumer = AsyncEventingBasicConsumer(channel)
    consumer.Received.AddHandler(AsyncEventHandler<BasicDeliverEventArgs>(fun sender args -> Task.CompletedTask))
    // ...

因为我得到以下错误：

Program.fs(10, 14): [FS1091] The event 'Received' has a non-standard type. If this event is declared in another CLI language, you may need to access this event using the explicit add_Received and remove_Received methods for the event. If this event is declared in F#, make the type of the event an instantiation of either 'IDelegateEvent<_>' or 'IEvent<_,_>'.

我检查了the official MS documentation，但看不到任何有关F＃的标准事件类型的引用。

Answer 1

F＃会将.NET事件公开为IEvent或IDelegateEvent类型的值，具体取决于事件声明和委托类型。只能对具有某些基本公共结构的事件执行此操作-当F＃无法执行此操作时，它将把事件的基础add和remove操作公开为可以直接调用的方法。

我不太确定什么是“标准事件类型”的规则。但是，您可以从the relevant bit of the F# compiler source code得到一些提示：

let TryDestStandardDelegateType (infoReader: InfoReader) m ad delTy =
    let g = infoReader.g
    let (SigOfFunctionForDelegate(_, compiledViewOfDelArgTys, delRetTy, _)) =
        GetSigOfFunctionForDelegate infoReader delTy m ad
    match compiledViewOfDelArgTys with 
    | senderTy :: argTys when (isObjTy g senderTy) && 
         not (List.exists (isByrefTy g) argTys)  -> Some(mkRefTupledTy g argTys, delRetTy)
    | _ -> None

因此，我的猜测是“标准事件类型”需要：

至少有一个参数
第一个参数的类型必须为object
没有byref参数

F＃的标准类型事件是什么？

1 个答案: