Recursive read of TCollection

Question

I'm very bad with recursion, never used it before. I know the theory of it .. not that that helps :)) For my problem i have a structure of TCollection that contains TCollection and TCollectionItem etc .. I have to write a recursion function that will read all my TCollectionItems. Here is graphical view:

TCollection->TCollectionItem(s)->TCollection->TCollectionItem(s)

TCollection can have 1 or even 2,3 TCollection's under him OR none.

Here are few more examples:

TCollection->TCollectionItem

TCollection->TCollectionItem->TCollection->TCollectionItem->TCollection->TCollectionItem

etc ..

Please tell me if i described the problem badly, i probably did .. please ask if something is unclear :)

Thanks for the support!

TCollectionItems owns a TCollection if it's Count property is larger then 0. — krizajb, Nov 05 '10 at 12:26
TCollectionItem does not have a Count property, and even if it did, it would not be incremented if the TCollectionItem owned its own child TCollection objects. — Remy Lebeau, Nov 11 '10 at 01:54

score 1 · Accepted Answer · answered Oct 29 '10 at 16:13

You haven't indicated the prototypes of the TCollection methods so as to enumerate and to read your TCollectionItems, and other needed details.

However, this is definitely solved by: The Composite Design Pattern.

The aim of this pattern is to traverse a recursive form, and to forward a call on a composite onto its composants and so on, until that reaches the leaves ( TCollectionItems with an empty TCollection in your case)

score 1 · Answer 2 · answered Nov 11 '10 at 02:12

The only way to recursively access child TCollection objects, without knowing the class types of the owning TCollectionItem objects so you can type-cast them, is to use the VCL's RTTI information.

In C++Builder versions prior to XE, VCL-based RTTI is only available for __published properties. Given a TCollectionItem (or any general TObject) object pointer, you can use the GetPropList() function declared in TypInfo.hpp to retreive a list of that object's published property information. You can then loop through that list, checking for any properties that report a TypeKind value of tkClass. When you find one, use the GetObjectProp() function to retreive that property's TObject pointer value, and then use dynamic_cast to make sure it is really a TCollection object before you access its child TCollectionItem objects.

In C++Builder 2010, a new Enhanced RTTI system was introduced, declared in Rtti.hpp, that provides information for all members of a class, including non-published properties and fields. With this enhanded RTTI, a child TCollection does not need to be declared as a __published property anymore. Under this system, you would use the TRttiContext class to access a TRttiType object for your recursion's starting TCollectionItem object, then use the TRttiType::GetFields() and TRttiType::GetProperties() methods to look for child TRttiField and TRttiProperty items that report a TypeKind of tkClass, then use the TRttiField::GetValue() and TRttiProperty::GetValue() methods to get the TObject object pointer that can be type-casted to a TCollection pointer with dynamic_cast.

Recursive read of TCollection

2 Answers2