CODEWITHSUNDEEP
memoryobjectcollectionsvb6dictionary
Austin S
Austin S

Reputation: 31

VB6 Collections/Object References

I was wondering if someone could tell what happens with regards to memory when the following happens:

Dict = New Dictionary --- Col = New Collection
Dict.Add Key, CustomClassOne
Dict.Add Key2, CustomClassTwo
Dict.Add Key3, CustomClassThree
Dict.Remove Key3
At this point is Key3 removed from memory or would I have to Set Dict.Item(Key3) = Nothing to remove it from memory?
Set Dict = Nothing '// will this remove All the above added custom class objects?
Set Col = Nothing '// Same question as above

Ugh VB memory management.... TY for your time, - Austin

Upvotes: 0

Views: 2896

Answers (2)

Martin Booth
Martin Booth

Reputation: 8595

VB is reference counted.

The rules of when an object is released from memory is simple.. it happens when there are no more references to that object. Each time an object goes out of scope (such as the end of a function) its reference count is decreased; which may in turn cause any objects which were referenced by this object to have their reference counts decreases too; and if their reference counts get to 0, they too are released from memory.

This is why there is usually no need to set an object's reference to Nothing... that will decrease its reference count, but that will also happen when it goes out of scope.

So to answer your question:

Dict.Remove Key3 is all that is required to remove CustomClassThree and Key3 from memory (as long as you don't have other references pointing to this object).

Set Dict = Nothing will remove everything from memory, but this would happen anyway when it goes out of scope (again assuming there are no other references pointing to the objects it contains).

Col doesn't seem to have much to do with the other statements and would be removed from memory when it goes out of scope without needing to set Col = nothing

Note:

The purpose of setting a reference to nothing is only really useful if you have objects which both have references to each other. Look up circular references for the details

Upvotes: 2

Bob77
Bob77

Reputation: 13267

With both Scripting.Dictionary and Collection instances when the last reference to the object is gone then the object references they hold are released. Whether or not the objects themselves are deallocated depends on whether or not another variable holds a reference to the same object.

Think of each reference as a rope holding a rock above an abyss. Until the last rope is cut the rock doesn't drop out of existence.

Removing an item from a Dictionary or Collection cuts that one rope.

Upvotes: 1

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