How to pass class as parameter?

[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

 

[Larry Lard]

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
....

 

[Brett]

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?

 

[Larry Lard]

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.