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c#.netf#
Joe Huha
Joe Huha

Reputation: 548

How do define an event in F# visible from C#

Looking at various bits of documentation, the way of defining an event in F# is to do something like 

type xyz () =
    let e = new Event<T>
    member x.something_happened : IEvent<T> = x.Publish

Unfortunately, the type of IEvent is really Miscrosoft.FSharp.Control.IEvent<_>, and it is hence difficult to use from within C#. Some articles suggest adding the CLIEvent attribute to member something_happended above but it seems to make no difference as far as its usability from C# without including the F# library goes.

How do I correctly define an event in F# so I can then add a delegate to it in C# code? Many thanks.

Upvotes: 3

Views: 497

Answers (1)

Daniel
Daniel

Reputation: 47904

There are two event types in F#, Event<'T> and Event<'Delegate, 'Args>. Only the second one is compiled to a .NET event when [<CLIEvent>] is present. Here's a working example:

type T() =
    let e = Event<EventHandler<_>,_>()

    [<CLIEvent>]
    member x.MyEvent = e.Publish

    member x.RaiseMyEvent() = e.Trigger(x, EventArgs.Empty)

In some cases the compiler generates a warning if [<CLIEvent>] is used with a non-standard event type. I'm not sure why it doesn't raise a warning for your code (perhaps a bug?).

Upvotes: 13

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