Re: How to implement strategy pattern with ATL Control?

I'm implementing a DVD clip player as a C++/ATL control that calls the
directshow API.I want to use the strategy pattern to implement three
almost identical ActiveX controls. The only difference is the
implementation of the function play.

I guess I will name the three different controls after the directshow
function used to implement the play function:
ClipPlayAtTimeInTitle
ClipPlayAtTime
ClipPlayAtTimeInTitleAutoStop

I want all these to inherit from an ActiveX control called ClipBase.

So I ran the ATL code generator in VS2005 and selected all the optional
choices and created a 419 line header file for ClipBase that defines
IClipBase and CClipBase.

I ran this again to create a control called ClipPlayAtTimeInTitle. I
gutted this file so it inherited from ClipBase. Now I get the following
error:

Error 3 error C3247: 'CClipPayAtTimeInTitle' : a coclass cannot inherit
from another coclass 'CClipBase'
c:\winoop\dvdclipeditorplayer\dvdplayer\dvdplayer\clippayattimeintitle.h
30

How do I use the strategy pattern in ATL?

I hope it is not necessary for ClipPlayAtTimeInTitle, ClipPlayAtTime and
ClipPlayAtTimeInTitleAutoStop to all define the same properties and call
backs. Uggghhh... that would be a huge amount of redundant code. Surely
there is a way to use the strategy pattern (as described in the book
"Design Patterns" by Gamma et. al)?

Thanks,
Siegfried
PS: Here is the code that caused the above error message:

// ClipPayAtTimeInTitle.h : Declaration of the CClipPayAtTimeInTitle

#pragma once

#include "resource.h" // main symbols

#include <atlctl.h>

#if defined(_WIN32_WCE) && !defined(_CE_DCOM) &&
!defined(_CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA)

#error "Single-threaded COM objects are not properly supported on Windows
CE platform, such as the Windows Mobile platforms that do not include full
DCOM support. Define _CE_ALLOW_SINGLE_THREADED_OBJECTS_IN_MTA to force ATL
to support creating single-thread COM object's and allow use of it's
single-threaded COM object implementations. The threading model in your
rgs file was set to 'Free' as that is the only threading model supported
in non DCOM Windows CE platforms."

#endif

#include "..\DVDClipBase\ClipBase.h"

// CClipPayAtTimeInTitle

[coclass,control,default(IClipBase,
_IClipBaseEvents),threading(apartment),vi_progid("DVDPlayer.ClipPayAtTimeInTitle"),progid("DVDPlayer.ClipPayAtTimeInTitle.1"),version(1.0),uuid("98D48207-ABF1-4103-BC72-450F62ED4E1E"),helpstring("ClipPayAtTimeInTitle
Class"),event_source(com),support_error_info(IClipPayAtTimeInTitle),registration_script("control.rgs")]

class ATL_NO_VTABLE CClipPayAtTimeInTitle :

public CClipBase{

public:

CClipPayAtTimeInTitle()

{

}

};