Well, it depends on how you need them to talk. You can pass an object into a method ByRef (passing a pointer), and as long as you don't store it in a module level variable, you don't really have a circular reference issue.

Basically VB is the same as working with COM in C++, with the exception that you control the reference counter in C++. VB handles the reference counting for you. The good news is that every reference is counted, and you have fewer details to track. The bad news is that you can't miscount purposefully.

Be careful if you go with the circular references, because you have to manage the cleanup well. I would try to keep the object structure as a tree, with references to the parent only. This way you can walk up & down the tree as needed, but you have clearly defined parent-child relationships for the purpose of top-down cleanup.

In 95% of the code I have done, I didn’t need circular references. In the other 5% I was always able to make a tree work (with a parent reference only). You can use the block to make the code easier to read, and less typing. They also run faster if you are making multple calls to an object that is more than one jump.

Example: lets say you have the following relationship.
 A->B->C->D (D is a child of C; C is a child of B; ...)

If you need D to look at the data in A, you could do the following:

Following code would be in D


John R Lick
[email protected]

John,

Yep - I think you are right. In my current application, I think that using this sort of tree structure is the most appropriate (making sure that I clean up systematically).

Thanks also for the coding tip.

Still happy to hear anyone else's views and experiences on this issue, if anyone wishes to contribute.

Cheers,

James

Dear James,
it is not that crazy as you think, you just hit one of the VB limitations. But we hardcore programmers do not like to say "no I cannot do it"... I like John's idea of the tree structure, even though it is not always possible. I am using a clean up method in (only) one of my projects and I hate it. Also consider that sometimes just redesigning the class structure it is possible to reduce if not eliminate the chating between classes (I was able to do it and not only in VB).
But I know that sometimes it is not possible to eliminate the circular reefrence: subclassing is an example, even though we are not supposed to subclass in VB are we :) In that case I used the weak reference method, and I liked it. This is how it works (all the code in classB)

private m_prtClass as Long

public property let(myOBJ as Objevt)
  m_ptrClass = ObjPtr(myObj)
end property

m_ptrClass is used only to store the address of classA, without creating cicular reference. When ClassA is needed:

dim ca as ClassA
CopyMemory ca m_ptrClass, 4

At this point ca holds a valid pointer without having incremented the reference count. The only trick is to release it via:

CopyMemory ca, &0, 4

before ca goes out of scope, otherwise VB will decrement the reference count by one automatically.

Marco

Marco,

Thanks. It's an interesting issue.

Thanks for this suggestion, and all your previous input. It's very helpful.

Regards,

James