... or a helper function that can be used on any TListBox without requiring
a modification introduced on a specific base class (easily adapted for other
control types, obviously)
uses
RTLConsts;
type
TListBoxHelper = class(TListBox);
TStringsHelper = class(TStrings);
function ListBoxGetObject(const aListBox: TListBox; const aIndex: Integer):
TObject;
begin
if (aIndex < 0) or (aIndex >= aListBox.Items.Count) then
TStringsHelper(aListBox.Items).Error(SListIndexError, aIndex);
result := TObject(TListBoxHelper(aListBox).GetItemData(aIndex));
end;
In this approach I separate the two entirely separate problems of an invalid
list index and an error in retrieving item data by specifically testing the
index for validity *before* attempting to retrieve the object. Whatever
errors might conceivably occur as a result of calling GetItemData() you at
least won't get a spurious and misleading "list index out of bounds".
> -----Original Message-----
> From: delphi-boun...@delphi.org.nz [mailto:delphi-
> boun...@delphi.org.nz] On Behalf Of Karl Reynolds
> Sent: Tuesday, 16 February 2010 11:16 a.m.
> To: NZ Borland Developers Group - Delphi List
> Subject: Re: [DUG] Is it a bug in latest version of Delphi?
>
> One way to get around this would be to add your own descendant of
> TListBox and add an Objects property that works as you would expect
> (ie. use that instead of items.objects). Here's a quick sample I
> knocked together:
>
> >>
> unit MyListBox;
>
> interface
>
> uses
> SysUtils, Classes, Controls, StdCtrls, RTLConsts;
>
> type
> TMyListBox = class(TListBox)
> private
> function GetObject(AIndex: Integer): TObject;
> procedure SetObject(AIndex: Integer; const AValue: TObject);
> { Private declarations }
> protected
> { Protected declarations }
> public
> property Objects[AIndex: Integer]: TObject read GetObject write
> SetObject;
> published
> { Published declarations }
> end;
>
> procedure Register;
>
> implementation
>
> type
> TIPRStrings = class(TStrings);
>
> function TMyListBox.GetObject(AIndex: Integer): TObject;
> begin
> Result := TObject(GetItemData(AIndex));
> if GetLastError <> 0 then
> TIPRStrings(Items).Error(SListIndexError, AIndex);
> end;
>
> procedure TMyListBox.SetObject(AIndex: Integer; const AValue: TObject);
> begin
> Items.Objects[AIndex] := AValue;
> end;
>
> procedure Register;
> begin
> RegisterComponents('Samples', [TMyListBox]);
> end;
>
> end.
> <<
>
> Alternatively, you could just use the relevant code yourself on your
> own listbox where you need to
>
> type
> TIPRCustomListBox = class(TListBox);
>
> procedure TForm1.Button1Click(Sender: TObject);
> var
> i: Integer;
> begin
> ListBox1.Items.AddObject('foo', TObject(-1));
> i := Integer(TIPRCustomListBox(ListBox1).GetItemData(0));
> if GetLastError <> 0 then // an error occurred, raise an exception or
> whatever
> else ShowMessage(IntToStr(i));
> end;
>
> Cheers,
> Karl
> _______________________________________________
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