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How to implement an event using EventHandlerList in F#?
eventhandlerlist

In C#, if i want to create a custom ASP.NET Control I did this:

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public class XXXX : Control{
   private static readonly object xxEventKey = new object();
   public event EventHandler xxEvent {
     add { this.Events.AddHandler(xxEventKey, value); }
     remove { this.Events.RemoveHandler(xxEventKey, value); }
   }

   protected virtual void OnXxEvent (EventArgs e){
     EventHandler handler = (EventHandler) base.Events[xxEventKey];
    if (handler != null)
    {
        handler(this, e);
    }
   }
}

base.Events is an instance of EventHandlerList, and is considered a good practice to use this instance in controls for a long time.

I'm working on a project of re-doing some webcontrols in F# for practice. It's possible doing this in F# for now? Thanks! PD: Sorry for my poor english!

.

It should be possible, I expect only syntax differences such as:

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EventHandler handler = (EventHandler) base.Events[xxEventKey];

becoming

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let handler = base.Events.[xxEventKey] :?> EventHandler
By on 2/26/2015 2:38 AM ()

Finally I could do it. I defined a custom event type that simulates F# Event types:

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type ControlEvent<'a when 'a :> EventArgs>(ehl : EventHandlerList, key)  =
    member this.Publish = 
        { new IDelegateEvent<EventHandler<'a>> with
              member x.AddHandler(handler) = 
                  ehl.AddHandler (key, handler)
              
              member x.RemoveHandler(handler) = 
                  ehl.RemoveHandler (key, handler) }

    member this.Trigger (sender, args) =
         match ehl.[key] with
            | :? EventHandler<'a> as hdl -> hdl.Invoke(this, args)
            | _ -> ignore()

And it's usage:

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type TextChangedEventArgs(oldValue, newValue) =
    inherit EventArgs()
    member this.OldValue = oldValue
    member this.NewValue = newValue

type TextBox() =
    inherit Control()
    static let textChangedKey = new obj();
    member private this.TextChangedEvent = new ControlEvent<TextChangedEventArgs>(base.Events, textChangedKey) 

    [<CLIEvent>]
    member this.TextChanged = this.TextChangedEvent.Publish

    member this.Text 
        with get () = this.ViewState.["Text"] :?> string
        and set (value : string) = 
            let oldValue = this.Text
            this.ViewState.["Text"] <- value
            this.TextChangedEvent.Trigger (this, new TextChangedEventArgs(oldValue, value))

And it works!! :D Best practices for clean code in F#?

By on 3/10/2015 9:45 AM ()

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