----- Original Message -----
From: "Dave Sellers" <[EMAIL PROTECTED]>
To: <[email protected]>
Sent: Friday, June 03, 2005 2:13 PM
Subject: [list] [delphi-en] TObjectList.Sort issues
> I'm using TObjectList.Sort successfully but, I suspect, not particularly
> elegantly. In fact, I have a suspicion I'm doing something dumb..
I've gone ahead and knocked up an extended TObjectList class, to support
object method comparison methods. Apologies if this source is longer than
should be posted to the list.
Regards
Walter
==================================
unit uObjectListEx;
{ 04/06/2005: The TObjectListEx extends TObjectList to allow slightly more
object
oriented delegation of the sort responsibility (ie, it expects an object
method to be
supplied to the Sort call, as opposed to a pure function pointer, as
present in TObjectList.)
A pure funtion pointer is sometimes problematic in contexts where the sort
operation requires access
to context held in an object. This extension help avoid some of that
awkwardness, though it
still requires typecasting in the supplied sort method to get at sort
object properties. }
interface
uses Contnrs;
type
TObjectListSortCompareMethod = function (Obj1, Obj2 : TObject) : Integer
of Object;
TObjectListEx = class(TObjectList)
private
procedure QuickSort(L, R: Integer;
SCompare: TObjectListSortCompareMethod);
public
procedure Sort(CompareMethod: TObjectListSortCompareMethod);
end;
implementation
{ TObjectListEx }
procedure TObjectListEx.QuickSort(L, R: Integer;
SCompare: TObjectListSortCompareMethod);
var
I, J: Integer;
P, T: Pointer;
begin
{ 04/06/2005: This method is based on QuickSort procedure from
Classes.pas, (c) Borland Software Corp.
but modified to be part of TObjectListEx class. It implements the
standard quicksort algorithm,
delegating comparison operation to an object method. The Borland
version delegates to a pure function
pointer, which is problematic in some cases.}
repeat
I := L;
J := R;
P := List^[(L + R) shr 1];
repeat
while SCompare(TObject(List^[I]), P) < 0 do
Inc(I);
while SCompare(TObject(List^[J]), P) > 0 do
Dec(J);
if I <= J then
begin
T := List^[I];
List^[I] := List^[J];
List^[J] := T;
Inc(I);
Dec(J);
end;
until I > J;
if L < J then
QuickSort(L, J, SCompare);
L := I;
until I >= R;
end;
procedure TObjectListEx.Sort(CompareMethod: TObjectListSortCompareMethod);
begin
if (List <> nil) and (Count > 0) then
QuickSort(0, Count - 1, CompareMethod);
end;
end.
==================================
unit uObjectListExTestForm;
{Demo/Test form for TObjectListEx}
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, uObjectListEx, StdCtrls;
type
// a little class used for demo/testing
TSortObj = class
Name : String;
constructor Create(AName : String);
end;
TObjectListExTestForm = class(TForm)
Memo: TMemo;
SortButton: TButton;
PopulateMemoButton: TButton;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure SortButtonClick(Sender: TObject);
procedure PopulateMemoButtonClick(Sender: TObject);
private
{ Private declarations }
FObjectlist : TObjectListEx;
function MyCompareMethod(Obj1, Obj2 : TObject) : Integer;
public
{ Public declarations }
end;
var
ObjectListExTestForm: TObjectListExTestForm;
implementation
{$R *.dfm}
{ TSortObj }
constructor TSortObj.Create(AName: String);
begin
Name := AName;
end;
{ TObjectListExTestForm }
procedure TObjectListExTestForm.FormCreate(Sender: TObject);
begin
FObjectList := TObjectListEx.Create;
FObjectList.OwnsObjects := True;
FObjectList.Add(TSortObj.Create('John'));
FObjectList.Add(TSortObj.Create('Peter'));
FObjectList.Add(TSortObj.Create('Zelda'));
FObjectList.Add(TSortObj.Create('Amelie'));
end;
procedure TObjectListExTestForm.FormDestroy(Sender: TObject);
begin
FObjectlist.Free
end;
procedure TObjectListExTestForm.SortButtonClick(Sender: TObject);
begin
FObjectlist.Sort(MyCompareMethod);
end;
function TObjectListExTestForm.MyCompareMethod(Obj1, Obj2: TObject):
Integer;
var
SortObj1, SortObj2 : TSortObj;
begin
SortObj1 := TSortObj(Obj1);
SortObj2 := TSortObj(Obj2);
result := CompareStr(SortObj1.Name, SortObj2.Name);
end;
procedure TObjectListExTestForm.PopulateMemoButtonClick(Sender: TObject);
var
ObjIndex : Integer;
begin
Memo.Lines.Clear;
for ObjIndex := 0 to FObjectlist.Count -1 do
Memo.Lines.Add(TSortObj(FObjectList[ObjIndex]).Name);
end;
end.
-----------------------------------------------------
Home page: http://groups.yahoo.com/group/delphi-en/
To unsubscribe: [EMAIL PROTECTED]
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/delphi-en/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
