Why does TObjectList<T>.Clear not free objects?
I just noticed that
var
ObjList : TObjectList <TMyObject>;
...
ObjList := TObjectList <TMyObject>.Create (True);
ObjList.Add (TMyObject.Create);
ObjList.Clear;
does not free the object. Looking at the source code it seems that no cnRemoved
notification is triggered in Clear
(inherited from TList <T>
).
My question: Is this intentional? Is there any reason why one does not want to get these notifications in the case of Clear
? Or can this be considered as a bug in the collection classes?
EDIT
Turns out that a I put the line
inherited Create;
on the top of TMyObject
destructor, which was supposed to go into the constructor. This is why I got memory leaks reported that looked like the TObjectList
was not freeing the items. And a look at the source convinced me (开发者_StackOverflowI was trapped by the Count
property). Thanks for your help anyway!
The list frees owned objects when you call .Clear
. You've got a testing error. The code sample below, written on Delphi XE, displays this:
Calling CLEAR
Object deleted.
Object deleted.
After CLEAR. Press ENTER to free L and Exit.
The code in TList<T>.Clear
is deceiving, because Count
is actually a property. Look at SetCount()
, then look at DeleteRange()
and you'll see the code for Notify(oldItems[i], cnRemoved)
at the end of the DeleteRange
procedure.
program Project3;
{$APPTYPE CONSOLE}
uses SysUtils, Generics.Collections;
type
TDelObject = class
public
destructor Destroy;override;
end;
{ TDelObject }
destructor TDelObject.Destroy;
begin
WriteLn('Object deleted.');
inherited;
end;
var L:TObjectList<TDelObject>;
begin
L := TObjectList<TDelObject>.Create(True);
L.Add(TDelObject.Create);
L.Add(TDelObject.Create);
WriteLn('Calling CLEAR');
L.Clear;
WriteLn('After CLEAR. Press ENTER to free L and Exit.');
Readln;
L.Free;
end.
TList<T>.Clear
calls DeleteRange
to do the work. The last part of DeleteRange
runs around all the items calling Notify
passing cnRemoved
.
Your analysis of the code is thus incorrect. The cnRemoved
notification is duly delivered and owned objects are freed.
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