Visual Basic - TypeOf??

Author

TypeOf??

Stephen J Bement

2004-03-29, 1:30 pm

Thanks, I take it that inheritance/polymorphism is implemented through sub
classing then?

Is there a way to tell if a class implements a certain interface?

Class Bubba
Implements IBarfly
Implements IPoet

Class Gwen
Implements IBarfly
Implements IKareokeist

Therefore:

Collection.Add New Gwen
Collection.Add New Bubba

For Each IBarfly in Collection
IBarfly.Drink 3
Next IBarfly

For Each Item in Collection
If Item = IPoet Then
Item.ReciteLimerick
ElseIf Item = IKareokeist Then
Item.Sing("Yellow Rose Of Texas")
End If
Next Item

--
Semper Fi,
Red

Please post to newsgroup only

Larry Serflaten

2004-03-29, 4:30 pm

"Stephen J Bement" <spam@null.net> wrote
> Thanks, I take it that inheritance/polymorphism is implemented through sub
> classing then?

I haven't bothered to look exactly how it is done, as long as it is
reliable, I can live with it being 'Black Box'...

> Is there a way to tell if a class implements a certain interface?

Dim Poet as IPoet
Dim Singer as IKareokeist

> For Each Item in Collection
> If TypeOf Item Is IPoet Then
Set Poet = Item
> Poet.ReciteLimerick
> ElseIf TypeOf Item Is IKareokeist Then
Set Singer = Item
> Singer.Sing("Yellow Rose Of Texas")
> End If
> Next Item

If you want to access the methods of an interface
then you have to declare a variable of that type of
interface.

LFS

Stephen J Bement

2004-03-29, 5:30 pm

But how do I tell if an object conforms to an interface?

If I were to:

Dim Singer as IKareokeist

Set Singer = Bubba

I would expect an error either during the assignment or at least when I try
to call Buuba.Sing() since Bubba::IBarfly,IPoet

"Larry Serflaten" <serflaten@usinternet.com> wrote in message
news:eZS3dEdFEHA.3448@TK2MSFTNGP09.phx.gbl...
>
> "Stephen J Bement" <spam@null.net> wrote
sub[color=darkred]
>
> I haven't bothered to look exactly how it is done, as long as it is
> reliable, I can live with it being 'Black Box'...
>
>
>
> Dim Poet as IPoet
> Dim Singer as IKareokeist
>
> Set Poet = Item
> Set Singer = Item
>
>
> If you want to access the methods of an interface
> then you have to declare a variable of that type of
> interface.
>
> LFS
>
>
>

Larry Serflaten

2004-03-29, 5:30 pm

"Stephen J Bement" <spam@null.net> wrote in message
> But how do I tell if an object conforms to an interface?

By testing it with TypeOf as was shown.

>
> If I were to:
>
> Dim Singer as IKareokeist
>
> Set Singer = Bubba
>
> I would expect an error either during the assignment or at least when I try
> to call Buuba.Sing() since Bubba::IBarfly,IPoet

It will error....

[color=darkred]

If it passes the TypeOf test, then you can use it, otherwise
it does not support that interface, and will error.

LFS

Ken Halter

2004-03-29, 5:30 pm

Did you try it? iirc, you should be getting a Type Mismatch error when the
'Set' runs. You'll definetly get a "procedure not found" type error if
there's no such procedure.

....and, actually, your code should look more like...
> Dim DrunkIdiot as IKareokeist
>
> Set DrunkIdiot = SlobberingAndFallingDown

--
Ken Halter - MS-MVP-VB - http://www.vbsight.com
Please keep all discussions in the groups..
"Stephen J Bement" <spam@null.net> wrote in message
news:uNwR5IdFEHA.4008@TK2MSFTNGP10.phx.gbl...
> But how do I tell if an object conforms to an interface?
>
> If I were to:
>
> Dim Singer as IKareokeist
>
> Set Singer = Bubba
>
> I would expect an error either during the assignment or at least when I
try
> to call Buuba.Sing() since Bubba::IBarfly,IPoet
>

Stephen J Bement

2004-03-29, 6:34 pm

Thanks alot for you help.
"Larry Serflaten" <serflaten@usinternet.com> wrote in message
news:OOIa6MdFEHA.3764@TK2MSFTNGP12.phx.gbl...
>
> "Stephen J Bement" <spam@null.net> wrote in message
>
> By testing it with TypeOf as was shown.
>
try[color=darkred]
>
> It will error....
>
>
>
>
> If it passes the TypeOf test, then you can use it, otherwise
> it does not support that interface, and will error.
>
> LFS
>
>

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