TObjectList appear in two units

2
votes

I am using Delphi XE3. When searching helps for TObjectList, I find it appears in two units:

http://docwiki.embarcadero.com/Libraries/Tokyo/en/System.Contnrs.TObjectList

and

http://docwiki.embarcadero.com/Libraries/Tokyo/en/System.Generics.Collections.TObjectList

In such a case, which unit should I include to use the class? Also what is the different between TObjectList and TList, I just see TObjectList = class(TList) in the first document so TObjectList is identical to TList?

Thanks

1
delphidelphi-xe3
One is generic, and one is not. TObjectList = class(TList) means that TObjectList inherits from TList, not that it is identical. Closer inspection of the documentation is needed. – David Heffernan

1 Answers

8
votes

System.Contnrs.TObjectList is the older legacy non-Generic version of a list of objects.

System.Generics.Collections.TObjectList<T> is the newer Generic version.

See Overview of Generics.

Use whichever one suits your needs.

The non-Generic TList is just a list of raw pointers. It does not do anything special with the pointers that are stored in it.

The non-Generic TObjectList is derived from TList to add extra handling of general purpose TObject pointers, such as to add the OwnsObjects property which allows the list to free stored objects when the list itself is freed.

The Generic TList<T> is similar to, but not derived from, the non-Generic TList, where T can be any type, it does not even need to be a pointer (for example, TList<Integer>).

The Generic TObjectList<T> is similar to, but not derived from, the non-Generic TObjectList, where T can be any class type that is derived from TObject.