Back to Questions
1.7k
views1
comment
How to trigger an event?
f#

Hi everyone,

I am having a hard time understanding how to raise an event in F#. I have read Don's article on events, and everything seemed to make sense except when I tried to write my own code :=) . I have put together a simple example that illustrates the problem.

type test_class = class

val mutable positions : int list

val class_changed : IEvent<int>

new() = {positions = []; class_changed = snd(IEvent.create())}

member x.add(i:int) = x.positions <- i :: x.positions;

x.class_changed // This class has been changed - this event should be flagged.

end

// Create a new object

let test_obj = new test_class();;

// Add a callback to this event

let _ = test_obj.class_changed.Add(fun i -> System.Windows.Forms.MessageBox.Show(i.ToString()) |> ignore);

// The event should be flagged.

do (test_obj.add(5)) ; (test_obj.add(10));;

When the class is changed, how are other objects made aware of the change?

I appreciate any help in this matter. Thanks

Chris

.

By calling:

snd(IEvent.create())

You are throwing away the value that is a function that can be used to raise the event. You need to say something like this (Originally posted to the F# mailing list by Don Syme):

type MyWidget = class

val tick : trigger<'a> * IEvent<'a>

new () = { tick = IEvent.create() }

// Trigger the event: often this member is hidden by a signature!

member x.OnMyEvent(ea) = (fst x.tick)(ea)

// Publish the event

member x.Tick = (snd x.tick)

end

let x = new MyWidget()

By on 8/16/2006 12:21 PM ()

    Topic tags

    IntelliFactory Offices Copyright (c) 2011-2012 IntelliFactory. All rights reserved.
    Home | Products | Consulting | Trainings | Blogs | Jobs | Contact Us | Terms of Use | Privacy Policy | Cookie Policy     		Built with WebSharper