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2377

answers:

2

I'm working on becoming as familiar with C# as I am with VB.NET (the language used at my workplace). One of the best things about the learning process is that by learning about the other language you tend to learn more about your primary language--little questions like this pop up:

According to the sources I've found, and past experience, a field in VB.NET that is declared as WithEvents is capable of raising events. I understand that C# doesn't have a direct equivalent--but my question is: fields without this keyword in VB.NET cannot raise events, is there a way to create this same behavior in C#? Does the VB compiler simply block these objects from having their events handled (while actually allowing them to raise events as usual)?

I'm just curious; I don't have any particular application for the question...

A: 

In C# you simply wouldn't add a handler for any events. Assuming the class has public events and we're not modifying it, you can't stop someone from adding an event handler.

Jon B
On the other hand, you simply have to define the eventHandler += yourHandler.
Will Marcouiller
+3  A: 

Omitting WithEvents doesn't block members from raising events, it just stops you from using the 'handles' keyword on their events.

Here is a typical use of withevents:

class C1
    public WithEvents ev as new EventThrower()
    public sub catcher() handles ev.event
        Debug.print("Event")
    end sub
end class

Here is a class which doesn't use WithEvents and is approximately equivalent. It demonstrates why WithEvents is quite useful:

class C2
    private _ev as EventThrower
    public property ev as EventThrower
        get
            return _ev
        end get
        set(byval value as EventThrower)
            if _ev isnot nothing then
                removehandler _ev.event, addressof catch
            end if
            _ev = value
            if _ev isnot nothing then
                addhandler _ev.event, addressof catch
            end if
        end set
    end property
    public sub new()
        ev = new EventThrower()
    end sub
    public sub catcher()
        Debug.print("Event")
    end sub
end class
Strilanc
I guess I'd never noticed that--probably because the only time I pay attention to it is when I get the error :-)
STW