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<div class=Section1>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Ideally yes.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Unfortunately you can get in trouble if
you let a TComponent descendent (eg TMyComponent) which is used normally on
your forms (eg streamed from the DFM) free itself when the interface reference
count reaches zero. The problem is that the VCL doesn’t create your
object as an interface and doesn’t maintain an interface pointer too it
(so ref count = 0). That’s OK… but the first time something (ie
your code) queries an interface from a TMyComponent (ref count = 1) and then
releases the interface (ref count = 0)… whoops, there goes your
TMyComponent, even though you didn’t want to release it and was still
necessary for your form.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>There are other possible issues, such as
keeping interface references to VCL created TComponents and then having the VCL
free your component when the form gets freed – even though you still have
an interface pointer to it. There are ways around these in specific cases but basically
if you want to keep pointers to TComponents then if at all possible they should
be as TComponent pointers, with Notify implemented by your owning object, etc
(ie the way the VCL does it).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>If Stacey is under control of all places
where his controls are created, who owns them, etc then fine, but if it is also
used as a normal TComponent then I would think twice.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>David.</span></font><font color=navy><span
style='color:navy'> <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'> </span></font><o:p></o:p></p>
</div>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
delphi-bounces@ns3.123.co.nz [mailto:delphi-bounces@ns3.123.co.nz] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Todd Martin<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, 29 September 2005
3:36 p.m.<br>
<b><span style='font-weight:bold'>To:</span></b> <st1:PersonName w:st="on">NZ
Borland Developers Group - <st1:place w:st="on">Delphi</st1:place> List</st1:PersonName><br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [DUG] How do you free
an Object Instance when you have anInterfaceReference?</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hi Stacey</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>You should never "free" an interface. </span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Implement reference counting in TMenuItem (see
TInterfacedObject). The object will be destroyed automatically, when all
variables that reference it (eg MyMenuItem) go out of scope.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Todd.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>----- Original Message ----- <o:p></o:p></span></font></p>
</div>
<blockquote style='border:none;border-left:solid black 1.5pt;padding:0cm 0cm 0cm 4.0pt;
margin-left:3.75pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt'>
<div style='font-color:black'>
<p class=MsoNormal style='background:#E4E4E4'><b><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial;font-weight:bold'>From:</span></font></b><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> <a
href="mailto:stacey@cjntech.co.nz" title="stacey@cjntech.co.nz">Stacey Verner</a>
<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><b><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial;font-weight:bold'>To:</span></font></b><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'> <a
href="mailto:delphi@ns3.123.co.nz" title="delphi@ns3.123.co.nz">NZ Borland
Developers Group - Delphi List</a> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><b><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial;font-weight:bold'>Sent:</span></font></b><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'> Thursday,
September 29, 2005 3:06 PM<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><b><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial;font-weight:bold'>Subject:</span></font></b><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'> [DUG] How do you
free an Object Instance when you have an InterfaceReference?<o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>If you have an object the implements and interface, and you
have a reference<br>
to the interface, how do you free the object using the reference to the
interface?</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I have the following (simplified) interface and classes.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>interface</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>type</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'> IMyMenuItem = interface<br>
function AddMenuItem(PCaption: String; POnClick:
TNotifyEvent): IMyMenuItem;<br>
procedure MyFree;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'> TMyMenuItem = class(TMenuItem, IMyMenuItem)<br>
public<br>
function AddMenuItem(PCaption: String; POnClick:
TNotifyEvent): IMyMenuItem;<br>
procedure MyFree;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'> TMyTBMenuItem = class(TTBItem, IMyMenuItem)<br>
public<br>
function AddMenuItem(PCaption: String; POnClick:
TNotifyEvent): IMyMenuItem;<br>
procedure MyFree;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>implementation;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>function TMyMenuItem.AddMenuItem(PCaption: String;
POnClick: TNotifyEvent): IMyMenuItem;<br>
var<br>
LMenuItem: TMyMenuItem;<br>
begin<br>
LMenuItem := TMyMenuItem.Create(PParent.Owner);<br>
LMenuItem.Caption := PCaption;<br>
LMenuItem.OnClick := POnClick;<br>
Result := LMenuItem;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>procedure TMyMenuItem.MyFree;<br>
begin<br>
Free;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>function TMyTBMenuItem.AddMenuItem(PCaption: String;
POnClick: TNotifyEvent): IMyMenuItem;<br>
var<br>
LMenuItem: TMyTBMenuItem;<br>
begin<br>
LMenuItem := TMyTBMenuItem.Create(PParent.Owner);<br>
LMenuItem.Caption := PCaption;<br>
LMenuItem.OnClick := POnClick;<br>
Result := LMenuItem;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>procedure TMyTBMenuItem.MyFree;<br>
begin<br>
Free;<br>
end;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>The intention of this is to allow you to dynamically create
menu items, but<br>
it doesn't matter if you have a normal menu (TMenuItem) or a<br>
Toolbar 2000 menu (TTBItem). You just deal with IMyMenuItem and the correct<br>
objects are created behind the scenes.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>This works pretty well except I have an intermittent access
violations when freeing.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>MyMenuItem: IMyMenuItem;</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>... // Do some stuff.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>MyMenuItem := RootMenuItem.AddMenuItem('Hello
World', HelloWorldClick);</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>... // Later on</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>MMyMenuItem.MyFree; // Intermiitent access violation
here!</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I don't actually like the fact that I have MyFree. It was
the only way I could think of doing it at the time.</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Stacey</span></font><o:p></o:p></p>
</div>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>Stacey
Verner
Ph: +64-9-4154790<br>
Software Developer Fax:
+64-9-4154791<br>
DDI: +64-9-4154797<br>
CJN Technologies Ltd. Email: </span></font><a
href="mailto:stacey@cjntech.co.nz"><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>stacey@cjntech.co.nz</span></font></a><br>
<st1:Street w:st="on"><st1:address w:st="on"><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>PO Box 302-278, North</span></font></st1:address></st1:Street><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'>
Harbour, <st1:City w:st="on">Auckland</st1:City> 1330, <st1:country-region
w:st="on"><st1:place w:st="on">New Zealand</st1:place></st1:country-region><br>
<st1:Street w:st="on"><st1:address w:st="on">12 Piermark Drive, North</st1:address></st1:Street>
Harbour, <st1:place w:st="on"><st1:City w:st="on">Auckland</st1:City>, <st1:country-region
w:st="on">New Zealand</st1:country-region></st1:place><br>
Visit our website at </span></font><a href="http://www.cjntech.co.nz/"><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'>http://www.cjntech.co.nz/</span></font></a><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'>
</span></font><o:p></o:p></p>
<div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center>
</span></font></div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>_______________________________________________<br>
<st1:place w:st="on">Delphi</st1:place> mailing list<br>
Delphi@ns3.123.co.nz<br>
http://ns3.123.co.nz/mailman/listinfo/delphi<o:p></o:p></span></font></p>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center>
</span></font></div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>No virus found in this incoming message.<br>
Checked by AVG Anti-Virus.<br>
Version: 7.0.344 / Virus Database: 267.11.8/113 - Release Date: 27/09/2005<o:p></o:p></span></font></p>
</blockquote>
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