How to pass class as parameter?

13 Apr 2005 2:30 PM

Brett

I have several classes that create arrays of data and have certain
properties. Call them A thru D classes, which means there are four. I can
call certain methods in each class and get back an array of data. All four
classes are the same except for the number of elements in their arrays and
the data.

I have a MainClass (the form), which processes all of these arrays. The
MainClass makes use of third party objects to do this. There are three
methods in the MainClass. Currently, I pass a parameter to these three
methods such as "A as string". This means to process class A. I have case
statements that take this parameter in the MainClass methods to know know
which class needs processing. There is much redundant code here since the
same processing is done for each class. It would be nice if I could just
pass in the class name as a parameter and run the code. Problem is I have
four classes instead of one and can't just pass them in as type class.

Should I place these four classes in a module? How else can I get around
using the case statements in the MainClass?

Thanks,
Brett

13 Apr 2005 3:46 PM

Larry Lard

Brett wrote:
Show quoteHide quote

> I have several classes that create arrays of data and have certain
> properties. Call them A thru D classes, which means there are four.
I can
> call certain methods in each class and get back an array of data.
All four
> classes are the same except for the number of elements in their
arrays and
> the data.
>
> I have a MainClass (the form), which processes all of these arrays.
The
> MainClass makes use of third party objects to do this. There are
three
> methods in the MainClass. Currently, I pass a parameter to these
three
> methods such as "A as string". This means to process class A. I
have case
> statements that take this parameter in the MainClass methods to know
know
> which class needs processing. There is much redundant code here
since the
> same processing is done for each class. It would be nice if I could
just
> pass in the class name as a parameter and run the code. Problem is I
have
> four classes instead of one and can't just pass them in as type
class.
>
> Should I place these four classes in a module? How else can I get
around
> using the case statements in the MainClass?

If you mean that A B C D all implement the 'same' methods, define an
interface IMyMethods containing these methods, and have A B C D all
Implement IMyMethods. Then where you currently pass "A" As String,
instead pass MyABCD As IMyMethods, and polymorphically invoke the
methods.

If you mean that A B C D don't all implement the 'same' methods, and
you're just looking for a more elegant syntax than passing "A" and
deducing you have an A, instead just pass o As Object, then find out
what you have been passed with lines like

If TypeOf o Is A Then
   Dim MyA As A = DirectCast(o, A)
   ' do the A stuff with MyA
ElseIf TypeOf o Is B Then
   Dim MyB As B = DirectCast(o, B)
   ' do the B stuff with MyB
....

--
Larry Lard
Replies to group please

13 Apr 2005 4:06 PM

Brett

Show quote Hide quote

"Larry Lard" <larryl***@hotmail.com> wrote in message
news:1113407173.231972.289250@o13g2000cwo.googlegroups.com...
>
> Brett wrote:
>> I have several classes that create arrays of data and have certain
>> properties. Call them A thru D classes, which means there are four.
> I can
>> call certain methods in each class and get back an array of data.
> All four
>> classes are the same except for the number of elements in their
> arrays and
>> the data.
>>
>> I have a MainClass (the form), which processes all of these arrays.
> The
>> MainClass makes use of third party objects to do this. There are
> three
>> methods in the MainClass. Currently, I pass a parameter to these
> three
>> methods such as "A as string". This means to process class A. I
> have case
>> statements that take this parameter in the MainClass methods to know
> know
>> which class needs processing. There is much redundant code here
> since the
>> same processing is done for each class. It would be nice if I could
> just
>> pass in the class name as a parameter and run the code. Problem is I
> have
>> four classes instead of one and can't just pass them in as type
> class.
>>
>> Should I place these four classes in a module? How else can I get
> around
>> using the case statements in the MainClass?
>
> If you mean that A B C D all implement the 'same' methods, define an
> interface IMyMethods containing these methods, and have A B C D all
> Implement IMyMethods. Then where you currently pass "A" As String,
> instead pass MyABCD As IMyMethods, and polymorphically invoke the
> methods.

I think this approach will work nicely. The method interfaces for the four
classes are the same. Any functions returning something are all the same
type. The only differences are inside of the methods, which is completely
encapsulated. Given this, can I still use the above technique?

Show quoteHide quote

>
> If you mean that A B C D don't all implement the 'same' methods, and
> you're just looking for a more elegant syntax than passing "A" and
> deducing you have an A, instead just pass o As Object, then find out
> what you have been passed with lines like
>
> If TypeOf o Is A Then
>   Dim MyA As A = DirectCast(o, A)
>   ' do the A stuff with MyA
> ElseIf TypeOf o Is B Then
>   Dim MyB As B = DirectCast(o, B)
>   ' do the B stuff with MyB
> ...
>
> --
> Larry Lard
> Replies to group please
>

14 Apr 2005 9:22 AM

Larry Lard

Brett wrote:
Show quoteHide quote

> "Larry Lard" <larryl***@hotmail.com> wrote in message
> news:1113407173.231972.289250@o13g2000cwo.googlegroups.com...
> >
> > Brett wrote:
> >> I have several classes that create arrays of data and have certain
> >> properties. Call them A thru D classes, which means there are
four.
> > I can
> >> call certain methods in each class and get back an array of data.
> > All four
> >> classes are the same except for the number of elements in their
> > arrays and
> >> the data.
> >>
> >> I have a MainClass (the form), which processes all of these
arrays.
> > The
> >> MainClass makes use of third party objects to do this. There are
> > three
> >> methods in the MainClass. Currently, I pass a parameter to these
> > three
> >> methods such as "A as string". This means to process class A. I
> > have case
> >> statements that take this parameter in the MainClass methods to
know
> > know
> >> which class needs processing. There is much redundant code here
> > since the
> >> same processing is done for each class. It would be nice if I
could
> > just
> >> pass in the class name as a parameter and run the code. Problem
is I
> > have
> >> four classes instead of one and can't just pass them in as type
> > class.
> >>
> >> Should I place these four classes in a module? How else can I get
> > around
> >> using the case statements in the MainClass?
> >
> > If you mean that A B C D all implement the 'same' methods, define
an
> > interface IMyMethods containing these methods, and have A B C D all
> > Implement IMyMethods. Then where you currently pass "A" As String,
> > instead pass MyABCD As IMyMethods, and polymorphically invoke the
> > methods.
>
> I think this approach will work nicely. The method interfaces for
the four
> classes are the same. Any functions returning something are all the
same
> type. The only differences are inside of the methods, which is
completely
> encapsulated. Given this, can I still use the above technique?

Sure thing. However... as a general principle, you should only do this
if the *meaning* of the method called and data returned are the same
across all the classes that will be implementing the interface.
Example: if we have CSupplier, CCustomer, CEmployee that all implement
IHaveAnAddress, and one of the interface methods is GetAddress
returning an array of String, then it would be misleading if, say,
CSupplier.GetAddress actually returned the last five order headers for
that supplier, even though the type would be correct.

If the semantics of the calls are different, I would say you're better
off checking the type with TypeOf ... Is and calling the different
methods with different names.

--
Larry Lard
Replies to group please