Re: Non-exposed interfaces - COM Discussion Boards

10-Aug-04 10:01

Could someone tell me what on Earth are 'non-exposed interfaces' ?

All I know is that a COM object can have interfaces, which can be accessed by using QueryInterface, for example. I would assume that an interface needs to be exposed by the object in order for QueryInterface to be able to retrieve it.

This problem relates to the Microsoft Knowledge Base Article Q281417 (Found here[^]) and the ability to accomplish the same on Visual C++. Even if I queried for any interface on the object, then queried for IUnknown and queried for the target interface, it always fails with E_NOINTERFACE.

Any ideas, suggestions or other ?

-Antti Keskinen

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The definition of impossible is strictly dependant
on what we think is possible.

Milton Karimbekallil10-Aug-04 18:53

10-Aug-04 18:53

I had gone thru Q281417. The term non-exposed they used in the sense non-creatable. That means u can not say
Private Obj As <big>new </big>IMsTscNonScriptable
Only thing u can do is to get a reference to an existing IMsTscNonScriptableobject in the terminal server client connection activex. ie,

Private Obj As IMsTscNonScriptable<br />
      set obj = MsTscAx1.Object

If u chk the IDL of the activex u can see the "noncreatable" keyword in the attribute section of IMsTscNonScriptable declaration. This noncreatable attribute will prevent a client from queryinterfacing that interface.

rgds..mil10

Antti Keskinen11-Aug-04 1:26

11-Aug-04 1:26

Thank you for the swift answer.

The next logical question is naturally: how to get this interface in the VC++ side. I tried looking for the ActiveX control in the Running Object Table, but it doesn't register itself there.. Also, using this method also requires you to use QueryInterface, which will result in a failure..

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Milton Karimbekallil11-Aug-04 3:23

11-Aug-04 3:23

Antti....

As per the MSDN sample code in vb we can get an existing IMsTscNonScriptable pointer as follows:

Private Obj As IMsTscNonScriptable<br />
set obj = MsTscAx1.Object

So the VC++ equivalent of the above code is:

CComPtr<IMsTscNonScriptable> pIMsTscNonScriptable;<br />
m_MsTscAx1.Object( reinterpret_cast<void**>(&pIMsTscNonScriptable) )

Here i assume u will insert the activex control into ur app and will add a member variable to it named m_MsTscAx1.

Unfrntly i don't have that ocx installed on my mechine. So i am not sure whethr it is a moniker provider and is supposed to be in the ROT.

hope this will help... rgds...mil10.

Antti Keskinen11-Aug-04 4:12

11-Aug-04 4:12

The ActiveX control was added to the dialog template, and I used 'Add Member Variable' to add a control variable into it. Visual Studio automatically generated the IDispatch wrapper class for the object. However, looking at the class declaration, it's derived from CWnd.

Thus, the member variable doesn't have a function called 'Object'. I tried attaching the CComPtr object into the m_MsTscAx1, and although this compiled properly, the attempt to call any methods resulted in an assertion.

Any more suggestions ?

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Antti Keskinen11-Aug-04 11:25

11-Aug-04 11:25

Problem solved.

As the m_MsTscAx1 is derived from CWnd, it also has a method called CWnd::GetControlUnknown, which returns a pointer to the existing IUnknown interface of the object. This interface pointer can be used to query for other existing interfaces on the object. Even those interfaces that are marked as 'non-creatable' can be accessed in this way, because querying for the interfaces doesn't create new interface objects.

The pointer returned by GetControlUnknown must not be released, as that might terminate the object (all interfaces released). However, all interfaces queried from here on should be released in the normal way. The key issue here is that QueryInterface only casts the given IUnknown pointer to the target interfaces, while adding the reference count at the same time.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Milton Karimbekallil11-Aug-04 20:09

OPC - implement the custom-DLL

11-Aug-04 20:09

its cooool man.. so u did it.

ur correct, noncreatable does not prevent from queryinterfacing an interface. More specifically noncreatable attribute is for a coclass, not for an interface. It just prevents that coclass from being instantiated. Also, if u r able to queryinterface that interface from the activex IUnknown, then that terminal cleint interface is not a separate coclass and not noncreatable attributed. I revoked the defenition i had given for a non exposed interface. I rephrase it as just another interfaec under the activex coclass, apart from the activex dispinterface and its event dispinterface.

What exactly it means is Scripting engins like Vbs need at least one IDsipatch derived interface. So normally COM servers that expect scripting engins as clients will always derive interfaces from IDispatch. But the limitation of COM is that a coclass can have only one IDispatch implimented interface.(Well, COM_INTERFACE_ENTRY2 is there to specify which Idispatch is 2 b considered) So if we need to have more than one interface in a coclass, then the remaining interfaces shud b iunknown derived (to make it compliant with vbs like apps). And As far as vb is concerned these IUnknown derived interfaces are "non exposed". That means vbs like clients can't get it directly, but they can queryinterface the IDispatch. If ur familiar with vb, u cud catch it easly. Or more clearly u can leave that term, it is specificaly for vb programmers we can say.

BTW GetControlUnknown is just an alternative to invoke mthds on an activex. As per the msdn sample the vb code gets the terminal cleint interface thru the objectmethod. if such a method is there in the activex, then ofcource that method will be there in the wrapper class also. coz, as u said wrapper class is just an idispatch wrapper for invoking methods on the activex. So it will contain all the methods in the activex. if u do a search for "object" in the wrapper class header file, it will be there. if it is not there, then that msdn sample code is wrong. i don't have that control installed on my mechine. generate the idl of that ocx and chk for "object" in the idl.

rgds...mil10

ro_bürgel9-Aug-04 23:45

ro_bürgel

9-Aug-04 23:45

I need a code example for a custom-DLL.
How get I access from a server to my I/O device?
My development environment is visual c++.
Thank you.
Ronny

Help: DCOM and local system account

Storm749-Aug-04 20:53

Storm74

9-Aug-04 20:53

A program I wrote in C++ is running under local system account (a service is executing it) in windows XP professional edition. The program is tiring to connect to a DCOM server located on the same PC and fails. This is the error information:

Product: Windows Operating System
ID: 10010
Source: DCOM
Version: 5.0
Component: System Event Log
Symbolic Name: EVENT_RPCSS_SERVER_START_TIMEOUT
Message: The server %1 did not register with DCOM within the
required timeout.
Explanation
The Component Object Model (COM) infrastructure tried to start the
named server; however, the server did not reply within the required
timeout period. There might be a deadlock, or the program might
not have responded to the server initialization code within the
timeout period of two minutes.

When I'm running the same program under a regular user account its work
perfectly. Why is that???

Thanks for your help

Re: Help: DCOM and local system account

Milton Karimbekallil9-Aug-04 22:55

Re: Help: DCOM and local system account

9-Aug-04 22:55

hi boss .. try this..

1) Run dcomcnfg.exe
2) Select ur Dcom server
3) Click properties
4) Goto security tab
5) Click on "Use custom access permissions"
5.1) Click on "Edit" button
5.2) Add "SYSTEM" account from the listbox
6) Click on "Use custom launch permissions"
7) Goto 5.1

rgds..mil10

Storm7410-Aug-04 2:58

Storm74

10-Aug-04 2:58

Thank alot for your help.

It works like a charm !!

Big Grin | :-D

Beginng Active-X. Need help.

lovehis9-Aug-04 20:47

lovehis

9-Aug-04 20:47

Hi, there.

I'm a Unix or embeded programmer and well... have good exp. with c/c++, assembler and whatever except "MS" things. Btw, now I have to do Active-X programming with VC. WTF!!! Cry | :((

So, I would like to ask you two questions:

1. Is it possible to learning Active-X without knowing COM or ATL, and with little bit VC exp.(Just little bit more than "hello world")?

2. Do you think "How long do I take to know Active-X"?

Please give a comment, suggestion or whatever... to me

Sorry for my poor English and Thank you for your help.

=^.^=

Re: Beginng Active-X. Need help.

Milton Karimbekallil9-Aug-04 23:10

Re: Beginng Active-X. Need help.

9-Aug-04 23:10

hi.. it is not possible to learn activex without knowing com and atl, but it is possible to do an activex using mfc app wizard , without knownig much abt com and atl. Just understand the basics of activex like method, properties and events. that will do... rgds...mil10

rgondzur12-Aug-04 9:36

rgondzur

12-Aug-04 9:36

If you are not limited to mfc, you will find ActiveX development much quicker using Visual Basic 6. Much of the lower level work is done for you and you can concentrate on your application specifics.

Instantiating another CoClass from a CoClass method in the same component

G. Raven9-Aug-04 7:44

G. Raven

9-Aug-04 7:44

Dear fellow CPians,

I have a simple COM component with two coclasses. I'd like to be able to instantiate one CoClass from a method of the other CoClass and be able to access the instantiated CoClasse's methods directly, and not through its interface (so I can supply it with some object data, not only basic data types).

Is there a way to do this? There should be, as the two CoClasses are under the same application and library. I only know the CoCreateInstance method, but with this method I only have access to the interface for the new created object.

Thanks in advance for your time with this.

Best regards.

G. Raven

Re: Instantiating another CoClass from a CoClass method in the same component

Milton Karimbekallil9-Aug-04 19:08