Equivalent of VB6's Public Not Creatable Class

[Wai-Yin Chee]

What would be equivalent to creating a Public Not Creatable class in VB.NET?


Wai-Yin Chee
wchee@sark.com

[Bob Butler]

"Wai-Yin Chee" <wchee@sark.com> wrote in message
news:3bb339cf$1@news.devx.com...
>
> What would be equivalent to creating a Public Not Creatable class in
VB.NET?

A Public Class with no Public constructor

[Rob Teixeira]

That is certainly the easiest way to implement it.

However, I believe that in VB6, you got the equivelant of an internal class,
but only the interface was written to the typelib (not the CoClass entry).
It was kind of a cludgy way of obscuring the line between class and interface.

You could also mimic that by creating a public interface and implementing
that interface in a Friend class. The difference here is that you need to
know within your application to instantiate a class with a different name
from the interface. So functionally, a class with only Friend constructors
is closer.

-Rob

"Bob Butler" <butlerbob@earthlink.net> wrote:
>
>"Wai-Yin Chee" <wchee@sark.com> wrote in message
>news:3bb339cf$1@news.devx.com...
>>
>> What would be equivalent to creating a Public Not Creatable class in
>VB.NET?
>
>A Public Class with no Public constructor
>
>
>

[Wai-Yin Chee]

Thanks for the responses! Here's what I have done. I'd like some feedback
on whether this is considered good practice:

At this point, I have created the 'Public Not Creatable' class as a Friend
class (ex: Class B) with functions that are declared Public. Within my application,
I have a Public Class (ex: Class A) that has a function called GetClassBObject()
that returns an Object interface which essentially returns the Class B interface.

From the UI, I am accessing Class B's interface this way:
Dim objA as New clsA()
Dim objB as Object

objB = objA.GetClassBObject()
'Drawback - intellisense is unavailable
objB.SomeMethod()

"Rob Teixeira" <RobTeixeira@@msn.com> wrote:
>
>
>That is certainly the easiest way to implement it.
>
>However, I believe that in VB6, you got the equivelant of an internal class,
>but only the interface was written to the typelib (not the CoClass entry).
>It was kind of a cludgy way of obscuring the line between class and interface.
>
>You could also mimic that by creating a public interface and implementing
>that interface in a Friend class. The difference here is that you need to
>know within your application to instantiate a class with a different name
>from the interface. So functionally, a class with only Friend constructors
>is closer.
>
>-Rob
>
>"Bob Butler" <butlerbob@earthlink.net> wrote:
>>
>>"Wai-Yin Chee" <wchee@sark.com> wrote in message
>>news:3bb339cf$1@news.devx.com...
>>>
>>> What would be equivalent to creating a Public Not Creatable class in
>>VB.NET?
>>
>>A Public Class with no Public constructor
>>
>>
>>
>

[Rob Teixeira]

The easier/more-correct way to do this is:

Public Class B
Friend Sub New()
MyBase.New
End Sub

' other methods/property here
End Class

Now, class B can only be created in the original project, but is fully accessable
in any other other project (without late binding).

-Rob


"Wai-Yin Chee" <wchee@sark.com> wrote:
>
>Thanks for the responses! Here's what I have done. I'd like some feedback
>on whether this is considered good practice:
>
>At this point, I have created the 'Public Not Creatable' class as a Friend
>class (ex: Class B) with functions that are declared Public. Within my application,
>I have a Public Class (ex: Class A) that has a function called GetClassBObject()
>that returns an Object interface which essentially returns the Class B interface.
>
>From the UI, I am accessing Class B's interface this way:
>Dim objA as New clsA()
>Dim objB as Object
>
>objB = objA.GetClassBObject()
>'Drawback - intellisense is unavailable
>objB.SomeMethod()
>

[Cali LaFollett]

> Thanks for the responses! Here's what I have done. I'd like some feedback
> on whether this is considered good practice:
>
> At this point, I have created the 'Public Not Creatable' class as a Friend
> class (ex: Class B) with functions that are declared Public. Within my
application,
> I have a Public Class (ex: Class A) that has a function called
GetClassBObject()
> that returns an Object interface which essentially returns the Class B
interface.
>
> From the UI, I am accessing Class B's interface this way:
> Dim objA as New clsA()
> Dim objB as Object
>
> objB = objA.GetClassBObject()
> 'Drawback - intellisense is unavailable
> objB.SomeMethod()

You should still be able to declare "Dim objB as clsB" you just can't go
"objB = New clsB" or "Dim obj As clsB = New clsB)because the "New" Friend
constructor method is not visible to your calling code.

Cal

[Me]

"Bob Butler" <butlerbob@earthlink.net> wrote:

>A Public Class with no Public constructor

Doesn't all classes by default have an public constructor inherited from
Object?

[Rob Teixeira]

If you override or shadow the default constructor, you can change the access
modifier (make it friend, private, etc.).

-Rob

"Me" <somewhere@earth.org> wrote:
>
>"Bob Butler" <butlerbob@earthlink.net> wrote:
>
>>A Public Class with no Public constructor
>
>Doesn't all classes by default have an public constructor inherited from
>Object?
>

[Bob Butler]

"Me" <somewhere@earth.org> wrote in message news:3bb36e67$1@news.devx.com...
>
> "Bob Butler" <butlerbob@earthlink.net> wrote:
>
> >A Public Class with no Public constructor
>
> Doesn't all classes by default have an public constructor inherited from
> Object?

AFAIK, constructors are not inherited. If you create a class with no
constructors then the compilers insert a default constructor which may give
you the same effect but as long as you create at least one Friend
constructor this does not happen.