[Resolved] Feature Request need lnDeleting in TList.Notify

[Zaher]

I inherited TObjectList, and used TList.Notify to work with my own hash list in the list, I need to recive deleted item before freed by Object List that own that items.
lnDeleted is call after this item really deleted and freed, I think  we need new one "lnDeleting" to call before deleting the item.

Code: [Select]

procedure TList.Delete(Index: Integer);
var P : pointer;
begin
  P:=FList.Get(Index);
  if assigned(p) then
    Notify(p, lnDeleting);
  FList.Delete(Index);
  if assigned(p) then
    Notify(p, lnDeleted);
end;

Thank in advance.

[ASerge]

I inherited TObjectList, and used TList.Notify to work with my own hash list in the list, I need to recive deleted item before freed by Object List that own that items.
lnDeleted is call after this item really deleted and freed, I think  we need new one "lnDeleting" to call before deleting the item.

Code: Pascal  [Select][+][-]

1. type
2.   TMyObjList = class(TObjectList)
3.   protected
4.     procedure Notify(Ptr: Pointer; Action: TListNotification); override;
5.   end;
6.  
7. procedure TMyObjList.Notify(Ptr: Pointer; Action: TListNotification);
8. begin
9.   if Action = lnDeleted then
10.     WorkWithItemBeforeFree(Ptr)
11.   else
12.     inherited;
13. end;

[Zaher]

Works now thank you so much.

I used this in another place, but I have complicated list inheritance and I got crash on removing line, It seem FPC compiler mess with me, It not recompile my changed unit (idk why)
I will mark as solved

[Thaddy]

The proper way is to use observer/observed:

Code: Pascal  [Select][+][-]

1. {$MODE OBJFPC}
2. {$APPTYPE CONSOLE}
3.  
4. uses Classes;
5.  
6. type
7.   TMyObject = class(TObject)
8.   strict private
9.     FName: string;
10.   public
11.     constructor Create(const AName: string);
12.     destructor Destroy; override;
13.   end;
14.  
15.   TFreeObjectObserver = class(TInterfacedObject, IFPObserver)
16.     procedure FPOObservedChanged(ASender: TObject; Operation: TFPObservedOperation; Data: Pointer);
17.   end;
18.  
19. constructor TMyObject.Create(const AName: string);
20. begin
21.   inherited Create;
22.   FName := AName;
23. end;
24.  
25. destructor TMyObject.Destroy;
26. begin
27.   Writeln(#9'Item ''', FName, ''' destroy');
28.   inherited;
29. end;
30.  
31. procedure TFreeObjectObserver.FPOObservedChanged(ASender: TObject; Operation: TFPObservedOperation; Data: Pointer);
32. begin
33.   if Operation = ooDeleteItem then
34.     TObject(Data).Free;
35. end;
36.  
37. procedure Test;
38. var
39.   L: TList;
40.   Observer: TFreeObjectObserver;
41. begin
42.   Observer := TFreeObjectObserver.Create;
43.   try
44.     L := TList.Create;
45.     try
46.       L.FPOAttachObserver(Observer);
47.       Writeln('Populate list');
48.       L.Add(TMyObject.Create('Zero'));
49.       L.Add(TMyObject.Create('One'));
50.       L.Add(TMyObject.Create('Two'));
51.       L.Add(TMyObject.Create('Three'));
52.       Writeln('Set item 0 to nil');
53.       L[0] := nil;
54.       Writeln('Delete item 2');
55.       L.Delete(2);
56.       Writeln('End of using list');
57.     finally
58.       L.Free;
59.     end;
60.   finally
61.     Observer.Free;
62.   end;
63. end;
64.  
65. begin
66.   Test;
67.   Readln;
68. end.

This is all standard code and supported by the RTL. Only dependency is classes.