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good methode to dublicate a TList

Posted on 2010-09-24
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Last Modified: 2012-05-10
I#m  working with 2 TList instances

I need a copy / clone of the orginal List,

only copy the List with Blist assign AList , but when I do freeList B also Items inside List A are free.

Any more flexible more general solution ?
BList .Assign(AList)  ;

my Solution :

procedure DublicateLists(ALIst, BList : TList)
begin

       for i := 0 to ALIst.Count -1 do 
          begin
                aListPtr := AList.Items[i];


               new (BListPtr);

               BLIstPtr^. .....   :=   ALitsPtr^. ......


               BList.add(BListPtr);
          
          end;
end;

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Question by:BdLm
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8 Comments
 
LVL 25

Expert Comment

by:epasquier
ID: 33752541
you can't with TList without knowing what kind of data it contains.
what do you put in your TList ?
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Author Comment

by:BdLm
ID: 33752574
inside the List  , aListPtr are stores  ,  defined as a record ;

aListPtr = record

      adata  : string;
      bdata  :  integer
      ......
  end;


won't read out the values of  AlIst // AListItemPtr  and copy value by value to a new BListItemPtr , that is the point
Solution sould be univeral and not only valid for my defined type of List Items

 

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LVL 9

Assisted Solution

by:auke_t
auke_t earned 100 total points
ID: 33752704
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LVL 25

Accepted Solution

by:
epasquier earned 400 total points
ID: 33752757
Here is a complete sample project that show how TList with pointers on records should be handled in those scenarios :
- creation
- deletion of 1 element, with item memory disposal
(TList.Delete would not free the memory pointed by the pointer stored in the list)
- element copy
- list destruction

Add will add a random item in first list. they are displayed like : HexaAddress ID Name
ex: 02099F78 0 AAFW
Use Ren and Del button with the item selected in the first list to rename and delete that item. You can then check that it did not alter the second list

Use Copy to clear the second list and copy all the first list in it

have fun !
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;

type
  TForm1 = class(TForm)
    btnAdd: TButton;
    lst1: TListBox;
    lst2: TListBox;
    btnDel: TButton;
    btnCopy: TButton;
    btnRen: TButton;
    procedure btnAddClick(Sender: TObject);
    procedure btnDelClick(Sender: TObject);
    procedure btnRenClick(Sender: TObject);
    procedure btnCopyClick(Sender: TObject);
  private
    { Déclarations privées }
    _NewID:Integer;
  public
    { Déclarations publiques }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

Type
  TRec=Record
        ID:Integer;
        Name:String;
       end;
  pRec=^TRec;

Var
 L1,L2:TList;

function ItemString( p:pRec ):String;
Var
 Name:String;
begin
 try
  Name:=p^.Name;
 except
  Name:='Err';
 end;
 Result:=Format('%8.8x %d %s', [Integer(p), p^.ID, Name]);
end;

function CopyRec(p:pRec):pRec;
begin
 New(Result);
 Result^:=p^;
// Move(p^,Result^,SizeOf(Result^)); do not use Move if you have strings
end;

procedure ShowItems(lb:TListBox;L:TList);
Var
 i:integer;
begin
 lb.Clear;
 for i:=0 to L.Count-1 do lb.Items.Add(ItemString(pRec(L[i])));
end;

procedure DeleteItem(L:TList;i:integer);
begin
 if (i<0) Or (i>=L.Count) Then Exit;
 try
  Dispose(pRec(L[i]));
 except
  ShowMessage('Error while deleting item '+IntToStr(i));
 end;
 L.Delete(i);
end;

procedure ClearList(L:TList);
begin
 while L.Count>0 do DeleteItem(L,L.Count-1);
end;

function RandomName:String;
Var i:integer;
begin
 Result:='';
 for i:=0 to 3 do Result:=Result+Char(Random(26)+65);
end;

procedure TForm1.btnAddClick(Sender: TObject);
Var
 NewItem:pRec;
begin
 New(NewItem);
 NewItem^.ID:=_NewID;
 Inc(_NewID);
 NewItem^.Name:=RandomName;
 L1.Add(NewItem);
 ShowItems(lst1,L1);
end;

procedure TForm1.btnDelClick(Sender: TObject);
begin
 if lst1.ItemIndex>=0 Then
  begin
   DeleteItem(L1,lst1.ItemIndex);
   ShowItems(lst1,L1);
   ShowItems(lst2,L2);
  end;
end;

procedure TForm1.btnRenClick(Sender: TObject);
begin
 if lst1.ItemIndex>=0 Then
  begin
   pRec(L1[lst1.ItemIndex])^.Name:=RandomName;
   ShowItems(lst1,L1);
   ShowItems(lst2,L2);
  end;
end;

procedure TForm1.btnCopyClick(Sender: TObject);
Var i:integer;
begin
 ClearList(L2);
 for i:=0 to L1.Count-1 do L2.Add(CopyRec(pRec(L1[i])));
 ShowItems(lst1,L1);
 ShowItems(lst2,L2);
end;

initialization
 L1:=TList.Create;
 L2:=TList.Create;
finalization
 ClearList(L1);
 ClearList(L2);
 L1.Free;
 L2.Free;
end.


// DFM

object Form1: TForm1
  Left = 412
  Top = 122
  Width = 428
  Height = 384
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  PixelsPerInch = 96
  TextHeight = 13
  object btnAdd: TButton
    Left = 8
    Top = 8
    Width = 60
    Height = 25
    Caption = 'Add'
    TabOrder = 0
    OnClick = btnAddClick
  end
  object lst1: TListBox
    Left = 8
    Top = 40
    Width = 185
    Height = 297
    ItemHeight = 13
    TabOrder = 1
  end
  object lst2: TListBox
    Left = 208
    Top = 40
    Width = 185
    Height = 297
    ItemHeight = 13
    TabOrder = 2
  end
  object btnDel: TButton
    Left = 72
    Top = 8
    Width = 60
    Height = 25
    Caption = 'Del'
    TabOrder = 3
    OnClick = btnDelClick
  end
  object btnCopy: TButton
    Left = 208
    Top = 8
    Width = 60
    Height = 25
    Caption = 'Copy'
    TabOrder = 4
    OnClick = btnCopyClick
  end
  object btnRen: TButton
    Left = 136
    Top = 8
    Width = 60
    Height = 25
    Caption = 'Ren'
    TabOrder = 5
    OnClick = btnRenClick
  end
end

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LVL 8

Author Comment

by:BdLm
ID: 33752762
:-)   excactly what I have been looking for !!!
0
 
LVL 25

Expert Comment

by:epasquier
ID: 33752770
If you like it much, you can raise points for this question :o) I did it just for you
0
 
LVL 8

Author Comment

by:BdLm
ID: 33759589
you helped bvery fast .....
0
 
LVL 8

Author Closing Comment

by:BdLm
ID: 33759593
very very fast response this time by ee forum ....  below 1 minute !!!!
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