"Matt F." wrote:

> I have an abstract class that about a dozen sub-classes inherit from.  I
> want to enforce that each sub-class shadows an event in the abstract class,
> but can't quite figure out how to do this.
>
> Basically, all of the inherited classes deal with data in some way or
> another.  I need to make sure that when the data is changed on any of those
> classes, they raise an event called "DataChanged", and have that enforced in
> some way from the abstract class.
>
> I've tried a number of approaches, including "MustOverride Event", which
> apparently isn't allowed.  Also, I've created an interface with just the
> DataChanged event, but there doesn't appear to be any sort of "Must
> Implement" available --- to make matters worse, when trying to raise an
> event from the inherited class on the abstract class, that doesn't appear to
> be allowed either.
>
> Obviously I can create an interface and just "remember" that every one of
> the sub-classes must implement this interface, but that's error prone and
> relies on me remembering additional steps, which obviously isn't a good
> idea.
>
> Any suggestions?
>
>
>

> I have an abstract class that about a dozen sub-classes inherit from.
> I want to enforce that each sub-class shadows an event in the abstract
> class, but can't quite figure out how to do this.
>
> Basically, all of the inherited classes deal with data in some way or
> another.  I need to make sure that when the data is changed on any of
> those classes, they raise an event called "DataChanged", and have that
> enforced in some way from the abstract class.
>
> I've tried a number of approaches, including "MustOverride Event",
> which apparently isn't allowed.  Also, I've created an interface with
> just the DataChanged event, but there doesn't appear to be any sort of
> "Must Implement" available --- to make matters worse, when trying to
> raise an event from the inherited class on the abstract class, that
> doesn't appear to be allowed either.
>
> Obviously I can create an interface and just "remember" that every one
> of the sub-classes must implement this interface, but that's error
> prone and relies on me remembering additional steps, which obviously
> isn't a good idea.
>
> Any suggestions?
>

"GhostInAK" <ghosti***@gmail.com> wrote in message
news:c71747b428a498c876ec61a0d2a6@news.microsoft.com...
> Hello Matt F.,
>
> It's quite simple really.  I chose to model a predatory animal for my
> example.. but the principles are there for your data manipulation classes.
> Define your event in an interface:
>
> Public Interface IPredator
>
> Event Eatten()
>
> End Interface
>
>
>
> Then create an abstract base class from which all others will inherit,
> which implements the interface:
>
> Public MustInherit Class Predator
> Implements IPredator
>
>
>
> Public Event Eatten(ByVal tSender As Object, ByVal tEatten As Object)
> Implements IPredator.Eatten
>
>
> Public Overridable Sub Eat()
>
> RaiseEvent Eatten()
>
> End Sub
>
> End Class
>
> Notice the Eat() sub.  It's sole job is to raise the Eatten event on our
> abstract class.
>
>
>
> Now create a subclass of our base class:
>
> Public Class Tiger
> Inherits Predator
>
>
>
> Public Overrides Sub Eat()
>
> MsgBox("Yummie")
> MyBase.Eat()
>
> End Sub
>
> End Class
>
>
>
> Here you see that the Eat() sub overrides the base implementation.  The
> last thing we do here is call the base class's Eat() method, which will
> raise the Eatten event.
>
> The eatten event is available on the subclass like so:
>
> Dim tTiger as Tiger = New Tiger
> AddHandler tTiger.Eatten, AddressOf some_event_handler
>
>
> Enjoy.
>
> -Boo
>
>
>
>
>> I have an abstract class that about a dozen sub-classes inherit from.
>> I want to enforce that each sub-class shadows an event in the abstract
>> class, but can't quite figure out how to do this.
>>
>> Basically, all of the inherited classes deal with data in some way or
>> another.  I need to make sure that when the data is changed on any of
>> those classes, they raise an event called "DataChanged", and have that
>> enforced in some way from the abstract class.
>>
>> I've tried a number of approaches, including "MustOverride Event",
>> which apparently isn't allowed.  Also, I've created an interface with
>> just the DataChanged event, but there doesn't appear to be any sort of
>> "Must Implement" available --- to make matters worse, when trying to
>> raise an event from the inherited class on the abstract class, that
>> doesn't appear to be allowed either.
>>
>> Obviously I can create an interface and just "remember" that every one
>> of the sub-classes must implement this interface, but that's error
>> prone and relies on me remembering additional steps, which obviously
>> isn't a good idea.
>>
>> Any suggestions?
>>
>
>