Hi Ian,
You are welcome. I like to monitor the group to keep my
programming skills sharp (either learning something or being able to
contribute). Good luck,
Tom

> -----Original Message-----
> From: delphigames@yahoogroups.com
> [mailto:delphigames@yahoogroups.com] On Behalf Of Ian Munro
> Sent: Wednesday, February 11, 2009 3:57 AM
> To: delphigames@yahoogroups.com
> Subject: RE: [DelphiGames] Casting an object to an interface
>
> Hello,
>
> Thanks for your help in this matter. I've
> been speaking to the programmer of the DLL and he thinks that
> he may be able to sort the ref count in his code. If this
> isn't possible I'll use your solution.
>
>
>
> Its good to see that there are still a couple
> of people monitoring this group.
>
>
>
> Ian
>
>
>
> From: delphigames@yahoogroups.com [mailto:delphigames@yahoogroups.com]
> On Behalf Of Grubb, Thomas G. (GSFC-583.0)
> Sent: Tuesday, February 10, 2009 7:40 PM
> To: delphigames@yahoogroups.com
> Subject: RE: [DelphiGames] Casting an object to an interface
>
>
>
> Hi Ian,
> Then you need to use _AddRef and _Release. This works great
> but you need to make sure that you call _Release *before* the
> listview deletes its items. Assuming you have a IVector
> interface and TMyVector class, the code below works to fill a
> listbox with interfaces and to be able to select an item and
> display the interface somewhere else. When the form closes,
> you will see a bunch of "Destroyed XXX" dialogs. If you
> comment out the FormClose, the vectors don't get properly destroyed.
>
> Tom
>
> procedure TForm1.FormCreate(Sender: TObject); var
> v: IVector;
> i: Integer;
> begin
> for i := 0 to 5 - 1 do
> begin
> v := TMyVector.Create;
> v.SetXYZ(Random(20)-10, Random(20)-10, Random(20)-10);
> v._AddRef; ListBox1.Items.AddObject(v.ToCommaString,
> TObject(v)); end; end;
>
> procedure TForm1.FormClose(Sender: TObject; var Action:
> TCloseAction); var
> I: Integer;
> begin
> for I := 0 to ListBox1.Items.Count - 1 do begin
> IVector(Pointer(ListBox1.Items.Objects[i]))._Release;
> end;
> end;
>
> procedure TForm1.ListBox1Click(Sender: TObject); begin if
> (Sender as TListBox).ItemIndex = -1 then Exit;
> Memo1.Lines.Text :=
> IVector(Pointer(TListBox(Sender).Items.Objects[TListBox(Sender
> ).ItemInde
> x])).ToCommaString;
> end;
>
> { TMyVector }
>
> destructor TMyVector.Destroy;
> begin
> ShowMessage('Destroyed '+ToCommaString); inherited; end;
>
>
> -----Original Message-----
> From: delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> [mailto:delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com> ] On Behalf Of Ian Munro
> Sent: Tuesday, February 10, 2009 10:26 AM
> To: delphigames@yahoogroups.com <mailto:delphigames%40yahoogroups.com>
> Subject: RE: [DelphiGames] Casting an object to an interface
>
> Hello,
>
> I should probably explain my problem in greater detail as
> using an interface list will not work for me. I need to
> populate a visible list of data (a listview or string grid)
> that a user can select from. Each item comes from an
> enumeration of IJanusDataSourceItem. I wanted to store each
> interface reference with each item in a listview control so
> that when the user presses a button I can easily grab the
> appropriate interface which contains further details. The
> data in the IJanusDataSourceItem's can change at runtime so
> the listview will change with new data being added or removed
> as well as the visual textual content being changed. I have
> no control over the IJanusDataSourceItem as these come from a
> C++ dll. If I use an interface list I then need to reference
> that list in my listview, I would also need to maintain the
> integrity between the two lists if data was added or removed.
> I hope that explains my problem a little better. The key
> point is that I need to show some data from the interface in
> a listview or string grid but also to be able to maintain a
> link between the visual content and the interface to update
> changes to the interface content etc.
>
> Ian
>
> From: delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> [mailto:delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com> ] On Behalf Of Grubb,
> Thomas G. (GSFC-583.0)
> Sent: Tuesday, February 10, 2009 3:17 PM
> To: delphigames@yahoogroups.com <mailto:delphigames%40yahoogroups.com>
> Subject: RE: [DelphiGames] Casting an object to an interface
>
> BTW, the problem you were having below is that when you
> shoved the interface into the Tlist, the reference count was
> not incremented. So, at some point, the object behind the
> interface got freed... And bang when you tried to get it
> back. You could have hacked around this by call __AddRef and
> all the other reference counting code but it would be a hack
> and messy. Much cleaner to use the TinterfaceList (which also
> has its own interface, IInterfaceList).
>
> Regards,
> Tom
>
> -----Original Message-----
> From: delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com>
> [mailto:delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com> ] On Behalf Of Grubb, Thomas G.
> (GSFC-583.0)
> Sent: Tuesday, February 10, 2009 10:08 AM
> To: delphigames@yahoogroups.com <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com>
> Subject: RE: [DelphiGames] Casting an object to an interface
>
> Hi Ian Munro,
> Use a TInterfaceList. That is a TList for interfaces.
> Regards,
> Tom
>
> -----Original Message-----
> From: delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com>
> [mailto:delphigames@yahoogroups.com
> <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com> ] On Behalf Of Ian Munro
> Sent: Tuesday, February 10, 2009 6:39 AM
> To: delphigames@yahoogroups.com <mailto:delphigames%40yahoogroups.com>
> <mailto:delphigames%40yahoogroups.com>
> Subject: [DelphiGames] Casting an object to an interface
>
> Hello,
>
> I need to store references to interfaces in a list so that
> when the user selects a list item I can easily access the
> interface that relates to that item. I've been casting the
> interface as a pointer and adding it as the list items
> object. Now when I try to retrieve it I try to cast it back
> and the compiler moans that you cant cast a TObject to an
> interface. I tried casting it to a pointer first and then to
> the interface type which the compiler likes (see code below).
> The problem I have then is that when the code runs, when the
> following line runs it throws an exception. My question is,
> Is there a better way to do what I need to do and what is
> causing the problem with this code. I must say that I'm not
> 100% when it comes to interfaces.
>
> Item := IJanusDataSourceItem (pointer (ListItemObject)) ;
>
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