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delphidelphi-2007tlist

Clear a TList or a TObjectList

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 that do this automatically from Free. Then I saw this from the doc of TList.Clear:

Call Clear to empty the Items array and set the Count to 0. Clear also frees the memory used to store the Items array and sets the Capacity to 0.

So it is basically the same. So

for TList

mylist.Clear;
myList.Free;

is the same as for TObjectList?

myList.Free;

Can TObjectList only be used for items as classes or can I store records?

Solution

  • 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.