I\'m a bit puzzled of what to use for storing objects in a list.
Until now I have used TList
and freed each item in a loop. Then I discovered TObjectList
Really watching the TObjectList
code in contnrs.pas OwnObjects
does nothing. FOwnObjects
is a variable declared in the private part of TObjectList
that is not used anywhere in the TObjectList
code (except just assigning the value), and there is no overridden Clear
procedure in it.
So I'm afraid it necessary to free the memory just the same as in TList
.
If you are using a recent version of Delphi I suggest that you use a generic list.
Right now you probably need to do a lot of casting when you use the objects from the list. With a generic list you don't have to do that anymore.
For instance if you have:
TMyObject = class(TObject);
Then you make the list like this:
TMyObjectList = TObjectList<TMyObject>;
There is an article in the Embarcadero Wiki:
http://docwiki.embarcadero.com/CodeExamples/XE8/en/Generics_Collections_TObjectList_(Delphi)
Read what the documentation is saying more carefully:
Clear also frees the memory used to store the Items array
Only the memory for the array itself is freed, not the memory used by individual elements inside the array.
It's not the same TList.Clear
only frees the memory allocated to store the pointers, not objects they are pointing to.
To avoid memory leaks you need to free the memory yourself - as you have been doing - or use TObjectList
.
To answer the second question, TObjectList
doesn't support storing records. You need to use TList
(or something else) in that case.
1. TList won't free the elements, with both Clear
or Free
.
aList.Clear;
Will just set aList.Count := 0
without freeing the aList.Items[]
elements. So you'll leak memory. You'll need an explicit free as such:
for i := 0 to aList.Count-1 do
TObject(aList[i]).Free;
But this is what TObjectList
does... :)
About TObjectList
, it is worth saying that TObjectList.Destroy
is calling Clear
.
So
aObjectList.Clear;
aObjectList.Free;
is exactly the same as
aObjectList.Free;
2. To store a list of records, you can use a dynamic array.
You'll get all TList
methods (and more) with our dynamic array wrapper. That is, Add / Delete / Clear / Count / IndexOf / Find
...
It has built-in serialization features (in binary or JSON), automated sorting and comparison (using RTTI) which are not existing with a TList/TObjectList
. From Delphi 5 and later.
With more modern version of Delphi, you may use generics to handle the dynamic array, if you do not want to use a third-party library.