Question

I need to create a descendant of TStringList class, which has the same functionality as TstringList class, but for each string/object from the list to have an id and subid elements.

Is this possible by inheriting the TStringList class, or I need to create a new class and implement the behavior I need.

LE: I also need the Objects property, so I can not store in the list a pointer to a structure.

Answer 1

From inspecting the TStringList class source, I think it is possible to inherit the TStringList class directly, by adding another FListIDs: PStringItemListIDs (similar to the FList: PStringItemList) where TStringItemIDs is a record of FID, FSubID: Integer (assuming data type is Integer).

Next you need to override each TStringList method that involves FList i.e.: Add, Clear, Delete, Insert, etc… where you will handle FListIDs being added or removed.

Finally create index properties: ID, SubID with getter and setter functions. e.g:

property ID[Index: Integer]: Integer read GetID write SetID;
property SubID[Index: Integer]: Integer read GetSubID write SetSubID;

The getter and setter functions will get or set FListIDs.