Delphi, how to free record in TList - delphi

Question

I want to know the best way to free a TList filled with record.
I have the following record:
type
TPkBill = record
PkBill: integer;
Constructor Create(c_PkBill: integer);
constructor TPkBill.Create(c_PkBill: integer);
begin
PkBill := c_PkBill;
end;
I create the list and fill it with the record:
procedure TfrmProject.lvBillDblClick(Sender: TObject);
var
i, iCount: integer;
item: TListItem;
oPkBill: TPkBill;
lstPkBill: Tlist;
begin
iCount := 0;
lstPkBill:= TList.Create;
//if an item is selected in lv
if (lvBill.ItemIndex = -1) then begin exit; end
else
begin
//Loop through all items and get selected item
for i := 0 to lvBill.Items.Count - 1 do
begin
item := lvBill.Items.Item[i];
if(item.Selected = true)then
begin
//create new item
oPkBill := TPkBill.Create(StrToInt(lvBill.Items[i].Caption));
//add it to a list
lstPkBill.Add(TObject(oPkBill));
//add up
iCount := iCount +1;
end;
end;
//Now we have a list ok pkBill
if(iCount > 1)then //other stuff I do
end
I want to be able to free the TList and also to free the record.
Here is what I already tried:
for i := 0 to lstPkBill.Count - 1 do
begin
//TObject(TPkBill(lstPkBill[i])).Free; //Acces violation at adress..
//FreeMem(TPkBill(lstPkBill[i])); //Incompatible types
//FreeMem(TObject(lstPkBill[i])); //Incompatible types
end;
lstPkBill.Clear;
FreeAndNil(lstPkBill);
Thanks you for the help, it's appreciated!

Answer 1

You have defined a record with a constructor. Calling a record constructor does not allocate memory on the heap, like a class constructor does. Your oPkBill variable exists on the stack. Calling oPkBill := TPkBill.Create(...) merely populates the members of that variable. You are then type-casting that entire variable (which only contains one Integer member) into a TObject pointer. You are not actually allocating any memory on the heap for the list item, so there is no need to free them.
I suspect what you were actually trying to do is something more like this:
type
PPkBill = ^TPkBill;
TPkBill = record
PkBill: integer;
Constructor Create(c_PkBill: integer);
end;
constructor TPkBill.Create(c_PkBill: integer);
begin
PkBill := c_PkBill;
end;
procedure TfrmProject.lvBillDblClick(Sender: TObject);
var
i: Integer;
item: TListItem;
oPkBill: PPkBill;
lstPkBill: TList;
begin
if lvBill.ItemIndex = -1 then Exit;
//an item is selected in lv
lstPkBill := TList.Create;
try
//Loop through all items and get selected items
for i := 0 to lvBill.Items.Count - 1 do
begin
item := lvBill.Items.Item[i];
if item.Selected then
begin
//create new item
New(oPkBill);
try
oPkBill^ := TPkBill.Create(StrToInt(lvBill.Items[i].Caption));
//add it to a list
lstPkBill.Add(oPkBill);
except
Dispose(oPkBill);
raise;
end;
end;
end;
//Now we have a list ok pkBill
if (lstPkBill.Count > 1) then
begin
//other stuff I do
end;
finally
for i := 0 to lstPkBill.Count - 1 do
Dispose(PPkBill(lstPkBill[i]));
lstPkBill.Free;
end;
end;