Unable to call AddRef() on IDispatch *
BLR CSG -- SAMAL_C1@blrv1.verifone.com
Thursday, January 02, 1997
Environment : VC++ 4.2-flat, Windows NT 3.51
Hi,
I have an OLE Local Server say Y.exe (written in VB), that serves an
Object say X. My client app is in VC++
I've created a wrapper class for this object using class wizard, say Cx.
Now i create an instance using
Cx m_x ;
m_x.CreateInstance("Y.X") ;
I'm able to call Interface fn. implemented by the VB program but if i call
m_x.AddRef() then i get a DISP_E_MEMBERNOTFOUND exception.
Also if i have a Interface fn. that returns another Object say GetObj(),
then I'm able to call GetObj() itself but an AddRef on the returned
LPINTERFACE fails. Some other fn. calls on this returned LPDISPATCH fails
with DISP_E_BADPARAMCOUNT.
Can anybody please help me out with what i'm doing wrong or not doing.
Thanks in advance
Samal Chandran.
ps. I'm very much an OLE novice.
hemantab@hclt.com
Tuesday, January 07, 1997
Hi ,
> I have an OLE Local Server say Y.exe (written in VB), that serves an
>Object say X. My client app is in VC++
>I've created a wrapper class for this object using class wizard, say
>Cx.
>
>Now i create an instance using
>Cx m_x ;
>m_x.CreateInstance("Y.X") ;
I am not sure whether i have been able to understand the above
properly, if not then pl clarify...anyway
If ur are using VC++ to create the wrapper class then i suppose u are
talking of IClassFactory::CreateInstance..... In that case the call to
CreateInstance should be preceded by a call to CoGetClassObject() to
get the IClassFactory interface. Then u can call
IClassFactory::CreateInstance with appropriate parameters. The
parameters also seem to be incorrect.
>I'm able to call Interface fn. implemented by the VB program
if u are planning to call other interface fns. from an EXE server then
i suppose u have the proxy and stub for marshalling in place.
> but if i call m_x.AddRef() then i get a DISP_E_MEMBERNOTFOUND
> exception.
AddRef should not doesn't throw any exceptions, coz normally AddRef()
implementation does not do any major stuff to throw exceptions. Maybe
ur m_x itself is not instantiated properly.
>Also if i have a Interface fn. that returns another Object say
>GetObj(), then I'm able to call GetObj() itself but an AddRef on the
>returned LPINTERFACE fails.
The function GetObj() should do the AddRef() before giving u the
interface pointer. Anyway as a general rule only when copying pointers
explicit AddRef() is needed, as otherwise all functions which return
an interface pointer must do a AddRef() before giving the pointer.
>Some other fn. calls on this returned
>LPDISPATCH fails with DISP_E_BADPARAMCOUNT.
I don;t think whatever i have written will be of much use, it will be
easier if u can give the sources to know what exacly ur doing, u can
attach all the sources to the mail and directly mail me at
hemantab@hclt.com.
Hemanta
___________________________________________________
Thought for the day:
Everyone should get married at sometime
Afterall happiness is not the only thing in life.
___________________________________________________
Thought for the day:
Concerto (n): a fight between a piano and a pianist.
BLR CSG -- SAMAL_C1@blrv1.verifone.com
Wednesday, January 08, 1997
Hi,
>> I have an OLE Local Server say Y.exe (written in VB), that serves an
>>Object say X. My client app is in VC++
>>I've created a wrapper class for this object using class wizard, say
>>Cx.
>>
>>Now i create an instance using
>>Cx m_x ;
>>m_x.CreateInstance("Y.X") ;
>I am not sure whether i have been able to understand the above
>properly, if not then pl clarify...anyway
>If ur are using VC++ to create the wrapper class then i suppose u are
>talking of IClassFactory::CreateInstance..... In that case the call to
>CreateInstance should be preceded by a call to CoGetClassObject() to
>get the IClassFactory interface. Then u can call
>IClassFactory::CreateInstance with appropriate parameters. The
>parameters also seem to be incorrect.
Yep u have misunderstood the environment - My OLE server is written in VB,
and the client I am writing in VC using MFC. So the wrapper i talk about is
the COleDispatchDriver derived one that automatically gets generated by
ClassWizard when i create a new class from OLE tlb/Exe/Dll. So the
CreateInstance is a member fn. of COleDispatchDriver and so the parameters
are right. I am getting an Interface * back.
>>I'm able to call Interface fn. implemented by the VB program
>if u are planning to call other interface fns. from an EXE server then
>i suppose u have the proxy and stub for marshalling in place.
The dispatch * returned is from the VB server and so should be an IDispatch
*, so VB should handle whatever marshalling is req. and also call the
required AddRef().
>> but if i call m_x.AddRef() then i get a DISP_E_MEMBERNOTFOUND
>> exception.
>AddRef should not doesn't throw any exceptions, coz normally AddRef()
>implementation does not do any major stuff to throw exceptions. Maybe
>ur m_x itself is not instantiated properly.
I know, that's why i feel that the IDispatch * i get is behaving funny.
Some Invokes work where as others don't.. I hope this clarifies my problem
------Rest of original post 'n reply ----------------
>Also if i have a Interface fn. that returns another Object say
>GetObj(), then I'm able to call GetObj() itself but an AddRef on the
>returned LPINTERFACE fails.
The function GetObj() should do the AddRef() before giving u the
interface pointer. Anyway as a general rule only when copying pointers
explicit AddRef() is needed, as otherwise all functions which return
an interface pointer must do a AddRef() before giving the pointer.
>Some other fn. calls on this returned
>LPDISPATCH fails with DISP_E_BADPARAMCOUNT.
I don;t think whatever i have written will be of much use, it will be
easier if u can give the sources to know what exacly ur doing, u can
attach all the sources to the mail and directly mail me at
hemantab@hclt.com.
Hemanta
Janakiraman M -- mjanaki@informix.com
Wednesday, January 08, 1997
At 09:07 AM 1/7/97 +0000, hemantab@hclt.com wrote:
>Hi ,
>
>> I have an OLE Local Server say Y.exe (written in VB), that serves an
>>Object say X. My client app is in VC++
>>I've created a wrapper class for this object using class wizard, say
>>Cx.
>>
>>Now i create an instance using
>>Cx m_x ;
>>m_x.CreateInstance("Y.X") ;
>
>I am not sure whether i have been able to understand the above
>properly, if not then pl clarify...anyway
>
>If ur are using VC++ to create the wrapper class then i suppose u are
>talking of IClassFactory::CreateInstance..... In that case the call to
>CreateInstance should be preceded by a call to CoGetClassObject() to
>get the IClassFactory interface. Then u can call
>IClassFactory::CreateInstance with appropriate parameters. The
>parameters also seem to be incorrect.
>
VC++ creates a Wrapper class which is derived from COleDispatchDriver. You
have to call its CreateDispatch Method with the Prog Id. first or
AttachDispatch if you already have a Dispatch.
>>I'm able to call Interface fn. implemented by the VB program
>
>if u are planning to call other interface fns. from an EXE server then
>i suppose u have the proxy and stub for marshalling in place.
>
>> but if i call m_x.AddRef() then i get a DISP_E_MEMBERNOTFOUND
>> exception.
>
This is the expected behaviour. The Class Cx does not expose a method called
AddRef() through OLE Automation and so you cannot call it. The wrapper class
Cx generated does not correspond to the IDispatch exposed by your server.
The actual IDispatch is stored as a member variable of COleDispatchDriver -
m_lpDispatch.
If you want to call AddRef, you should call it on m_x.m_lpDispatch->AddRef()
and not m_x.AddRef()
>AddRef should not doesn't throw any exceptions, coz normally AddRef()
>implementation does not do any major stuff to throw exceptions. Maybe
>ur m_x itself is not instantiated properly.
>
>>Also if i have a Interface fn. that returns another Object say
>>GetObj(), then I'm able to call GetObj() itself but an AddRef on the
>>returned LPINTERFACE fails.
>
This is probably because of the same reason.
>The function GetObj() should do the AddRef() before giving u the
>interface pointer. Anyway as a general rule only when copying pointers
>explicit AddRef() is needed, as otherwise all functions which return
>an interface pointer must do a AddRef() before giving the pointer.
>
>>Some other fn. calls on this returned
>>LPDISPATCH fails with DISP_E_BADPARAMCOUNT.
>
>I don;t think whatever i have written will be of much use, it will be
>easier if u can give the sources to know what exacly ur doing, u can
>attach all the sources to the mail and directly mail me at
>hemantab@hclt.com.
>
>Hemanta
>___________________________________________________
>Thought for the day:
>Everyone should get married at sometime
>Afterall happiness is not the only thing in life.
>
>
>___________________________________________________
>Thought for the day:
> Concerto (n): a fight between a piano and a pianist.
>
>
>
hemantab@hclt.com
Tuesday, December 10, 1996
Hi,
>Yep u have misunderstood the environment - My OLE server is written
>in VB, and the client I am writing in VC using MFC. So the wrapper i
>talk about is the COleDispatchDriver derived one that automatically
>gets generated by ClassWizard when i create a new class from OLE
>tlb/Exe/Dll. So the CreateInstance is a member fn. of
>COleDispatchDriver and so the parameters are right. I am getting an
>Interface * back.
Its not CreateInstance, its CreateDispatch in case u want to load the
object and get an instance pointer , or use AttachDispatch if u
already have a dispatch pointer...
CreateInstance is a member of IClassFactory interface, so i am not
confused, the confusion is at ur end.
>The dispatch * returned is from the VB server and so should be an
>IDispatch *, so VB should handle whatever marshalling is req. and
>also call the required AddRef().
Yeah actually if ur using only standard interfaces like IUnknown ,
IDispatch etc. etc. etc. the marshalling is already there in
compobj.dll. But in case of custom interfaces u have to use MIDL to
generate the proxy and stub.In ur case i think ur talking of
IDispatch only so things should be definitely fine.
>I know, that's why i feel that the IDispatch * i get is behaving
>funny. Some Invokes work where as others don't.. I hope this
>clarifies my problem
i can only think of one case where this can happen, ur telling that
ur Invoke fails saying some DISP_E_MEMBERNOTFOUND, that exception is
normally thrown by IDispatch::GetIDsOfNames(). The implementation of
GetIDsOfNames() normally has an array of function names and when the
function name if passed to the function it returns a dispid which is
used in a switch in Invoke() to invoke a method.
So if it returns a exception DISP_E_MEMBERNOTFOUND that means (as far
as my knowledge goes) ur implementation of GetIDsOfNames() is where
the problem lies.
I don't know what is done in VB , but in VC the GetIDsOfNames() is
embedded as a macro DECLARE_DISPATCH_MAP .......
A small doubt maybe ur sending name as a char and ur VB server
expects UNICODE....that's a small problem but can be a major pain (i
have faced it).
It will be easier if u can send me the code both client as well as
server.
Bye
Hemanta
___________________________________________________
Thought for the day:
Make a software idiot proof and someone will make a better idiot.
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