C++ unable to access COM object, but VB can? - COM Discussion Boards

9-Jan-04 11:13

Tip: if you ever get a HRESULT which you don't recognize, do a "find in files" through your system include files. It's bound to be there, somewhere with a symbolic name. Smile | :)

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If there was a problem, Yo, I'll solve it!
Check out the hook while my DJ revolves it.

DCOM

rajusnair9-Jan-04 4:50

rajusnair

9-Jan-04 4:50

How can i deploy a MTS Server

when i am using com componnets to connect remote com object it giving the error interface not supported

Memory Leakage.

JigarThakkar8-Jan-04 22:49

JigarThakkar

8-Jan-04 22:49

hello,

I have made one COM, which returns network groups, users etc. When i run it, (use it in vb) it will crash. It runs function once but if then i press anything it will crash.

Can anybody please help me?

Thanx a Lot.

Jigar. Confused | :confused:

Re: Memory Leakage.

Jörgen Sigvardsson9-Jan-04 9:41

9-Jan-04 9:41

Did you AddRef() the interface pointer before returning it? I'm assuming you're passing an interface pointer to VB as a [out, retval] parameter.

If not, you better read up on the rules of COM. Smile | :)

--
If there was a problem, Yo, I'll solve it!
Check out the hook while my DJ revolves it.

COM client in VB

Member 8040808-Jan-04 18:24

Member 804080

8-Jan-04 18:24

hi i want to know how a COM Component developed in Visual c++ using ATL Library , will be invoked in Visual Basic so that the connection to the Object remains active means server can send information to client with out client call to server.

Same like the IConnectionPoint. Advise () so in vc++.
NOT Like this
Confused | :confused:

Dim WithEvents obj As Word.Application
...
Set obj = New Word.Application

regards
shahzad

Re: COM client in VB

Jörgen Sigvardsson9-Jan-04 9:50

C++ unable to access COM object, but VB can?

9-Jan-04 9:50

You need to implement a source interface in your COM object via IConnectionPointContainer. The ATL wizard will do this for you. I can't remember how it works in VC6, but in VS.NET, you can check "Connection Points" on the "Options" page of the wizard.

The wizard will give you an interface IYourInterface. This is the interface you specified for your object. It will also give you a dispinterface called _IYourInterfaceEvents. This is the source interface which VB will recognize with WithEvents.

Just add your event functions in that interface. Then when you are done (or whenever you modify this interface), right click on your COM class in the Class View, and select "Add -> Add Connection Point". The IDE will now generate (or update if you've done this before) the proxy class for firing the events (resides in the file _IYourInterfaceEvents_CP.h). This template class is inherited by your COM class (the wizard set this up, you don't have to do it manually). It provides Fire_XXX-functions for you to use within the methods of your COM class. If you have defined an event like this: void OnEvent(long x, BSTR y), the corresponding firing function will look like this: Fire_OnEvent(long x, long y). If you call such a fire function, the proxy class will automatically call all event sinks with the parameters you provided.

Was this what you needed to know?

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If there was a problem, Yo, I'll solve it!
Check out the hook while my DJ revolves it.

Nathan Brown8-Jan-04 11:27

8-Jan-04 11:27

Hello, I am having a frustrating problem. While I am not an expert in COM, I have done my share.

I am trying to connect to a program that exposes an ActiveX interface, it supplies the Type Library file (.tbl) which I have imported into my C++ project, however, it does not register its self with the registery. Also, there isn't a CLSID available. So none of the normal C++ functions work. Did I mention that accessing it through VB works? (well VBscript).

It ends up that the program I am trying to access only registers in OLE's Running Object Table. I can use CoGetObject() (of course there isn't many examples of it) to find it, but then my program is unable to call the functions and crashes when m_lpDispatch->Invoke() is called in the InvokeHelper function.

My CoGeObject looks like this:

BIND_OPTS bind_op;
// ... fill out the options.
REFIID riid = IID_IDispatch;
IBACtalkActiveXInterface * p_ibac = NULL;      // Use class constructed from Type Library

int result = CoGetObject(OLESTR("bactalk.activex.interface"), &bind_op, rrid, (void **)&p_ibac);  // this succeeds when the program is running

p_ibac->SendTimeSync();         // crashes inside of COleDispatchDriver::InvokeHelper(...)

I'm not sure what is going on. My main question is why does it work in VB and not in C++. Arg. I've tried everything I can think of, so any insight would be most helpful. Should I not use the COleDispatchDriver derived class any more?

Thanks,
Nathan Brown

Vi28-Jan-04 21:24

Vi2

8-Jan-04 21:24

If it works in VB, then it should work in C++, because the C++ is more powerful than VB (VBS etc). But not vice versa Wink | ;)

.

Can you give some VB code working well for you?

With best wishes,
Vita

Nathan Brown9-Jan-04 13:12

9-Jan-04 13:12

Hello, I would have though that C++ wouldn't have this problem. A sample bit of code that they give, and that I have tested (in VB script) is this:

Dim bt As Object
Set bt = GetObject ( "BACtalk.ActiveX.Interface" )
bt.SendTimeSync

I just can't make the same thing work in C++. Is there some magic function I should be using? I thought I was getting somewere with CoGetObject(), but no. Any further help would be aprecciated. If I had a choice, I would probably do this in C# and it would work.

Nathan Brown

Vi211-Jan-04 21:02

Vi2

11-Jan-04 21:02

Try to use this fragment of code. If it doesn't work, try to check the hr value and tell this value to us.

BIND_OPTS bind_op;
// ... fill out the options.
REFIID riid = IID_IDispatch;
IDispatch* p_ibac = NULL;
HRESULT hr = CoGetObject(OLESTR("bactalk.activex.interface"), &bind_op, rrid, (void **)&p_ibac);
if( SUCCEEDED(hr) )
{
//p_ibac->SendTimeSync();         // crashes inside of COleDispatchDriver::InvokeHelper(...)
	LPOLESTR lpsz = OLESTR("SendTimeSync");
	DISPID dispid;
	hr = p_ibac -> GetIDsOfNames(IID_NULL, (LPOLESTR*)&lpsz, 1, LOCALE_USER_DEFAULT, &dispid);
	if( SUCCEEDED(hr) )
	{
		DISPPARAMS dispparams = { NULL, NULL, 0, 0};
		VARAINT varRet;
		VariantInit(&varRet);
		hr = p_ibac -> Invoke(dispid, IID_NULL, LOCALE_USER_DEFAULT,
			DISPATCH_METHOD|DISPATCH_PROPERTYGET, &dispparams, &varRet, NULL, NULL);
		VariantClear(&varRet);
	}
}

With best wishes,
Vita

Nathan Brown27-Jan-04 13:37

27-Jan-04 13:37

Thanks for the help and encouragement. What ended up working is calling CoGetObject() with IID_IUnknown first, then querying for the IID_IDispatch interface. For whatever reason, I can't have the IID_IDispatch in the CoGetObject and expect anything to work, even an IUnknown level function.

Nathan Brown

Jörgen Sigvardsson9-Jan-04 9:57

9-Jan-04 9:57

Is the COM object you are trying to connect to via the ROT an out-proc server? If so, make sure you've registered the proxy server dll for that server.

I meddled with the ROT a week ago, and experienced similar strange behaviors. I access the ROT directly with monikers and the IRunningObjectTable interface, but that's basically what happens inside the CoGetObject() function anyhow. Anyway, it seemed to me that I got either a malfunctioning proxy or a proxy for the wrong interface. Don't ask how I have these clues, long story.. But one would think that I'd get a E_XXX back from the ROT if it can't give me a correct proxy.

Anyhow, I built a proxy server dll for the out-proc server, registered and everything worked just fine.

--
If there was a problem, Yo, I'll solve it!
Check out the hook while my DJ revolves it.

Nathan Brown9-Jan-04 13:22

9-Jan-04 13:22

I had seen your message on that before I posted, but I wasn't sure if it was the same problem. Also, I don't understand exactly what you were explaining.

How does a proxy DLL work? More importantly, are there any examples of one available?

If you are talking about something that came with the application I am trying to interface, then I don't know of any proxy DLLs. I tried registering any DLLs that looked like they might register, and also the .exe (with -RegServer), but none of that worked.

Thanks for any help.

Nathan Brown

Jörgen Sigvardsson9-Jan-04 13:34

How to bypass login window?

9-Jan-04 13:34

Nathan Brown wrote:
How does a proxy DLL work? More importantly, are there any examples of one available?

A proxy DLL contains code for the proxy and stub for one or more interfaces. Whenever you make a COM call across an apartment boundary (between "threads" and processes (local or network)), the data passed back and forth must be marshalled - especially between processes since they do not share memory. Now, there's a lot of details here which I will not go into (mainly because I don't I'm competent enough to give a good explanation, and a forum post is way too short). I advise you to pick up a book on the subject - Don Box' Essential COM is a good read.

Nathan Brown wrote:
If you are talking about something that came with the application I am trying to interface, then I don't know of any proxy DLLs.

Ah, so you haven't written this app yourself? I see. Well, I've read that sometimes the proxy/stub DLL is not needed. The system itself should be able to "compile a proxy/stub" on the fly for any OLE automation compatible interface described in a TLB (.DLL, .EXE, .OCX, or .TLB). But contrary to this statement (can't remember if I read it in MSDN or Don Box' Essential COM), it does not always work. So basically, for your particular problem (no source for the application/automation server), I do not know a solution. Frown | :(

However, the proxy/stub DLL I was talking are normally built with DLL-servers by default. Try generating such a project and take a look at the proxy/stub project which is automatically attached to the solution.

--
If there was a problem, Yo, I'll solve it!
Check out the hook while my DJ revolves it.

SiddharthAtw7-Jan-04 18:23

SiddharthAtw

7-Jan-04 18:23

I want to write user name and password in login window of Yahoo messenger from my application.
Till now I am able to get Handle to Login window using Getclass and GetwindowText.My plan is to get the handle of Login window , then that of edit boxes of Login window. Then to paste text into edit boxes. The problem is how to know whether this login (which is a dialog box) or edit boxes belongs to Yahoo messenger or a particular window.

A property of a user defined ATL class

Gush6-Jan-04 12:23

Gush

6-Jan-04 12:23

I'm trying to add a property to a "COleControl" derived control. The problem is that the type of that property is another ATL Class in the same project, and I don't seem to know how to do that.

Anyone has any ideas?

Gush

How to use IWMPPluginUI::TranslateAccelerator?

IGx896-Jan-04 5:07

IGx89

6-Jan-04 5:07

I'm working on a background UI plugin for WMP9, and I'm wanting to add custom hotkeys. Looking through the documentation, it appears that the IWMPPluginUI::TranslateAccelerator(LPMSG lpmsg) function would work the best for that; but, unfortunately, I have no idea how to notify WMP9 of my accelerator table. How should one go about doing that?

Tutorial on COM

Omar Alvi5-Jan-04 4:45

Omar Alvi

5-Jan-04 4:45

HEllo people,

I am a begineer at COM and i am facing difficulties in understanding it. I wanna learn to make components without using ATL and MFC first. CAn anyone direct me to some good resource no the net, which along with the theory guides you how to make a component step by step. Most of the articles that i have come across are in theory too much and implemetation is not dicussed in that detail.

Thank you...

Re: Tutorial on COM

valikac5-Jan-04 4:59

valikac

5-Jan-04 4:59

Check out MindCracker.

http://www.mindcracker.com/mindcracker/c_cafe/com.asp

Check out MSDN.

Kuphryn

COM & VB.NET overloading

izotov5-Jan-04 2:36

izotov

5-Jan-04 2:36

Hi,

I'm working on a VB.NET project and my objects should be reachable using COM. My problem is that these objects have overloaded methods, properties, which seems problematic.

For example I have a collection class with two item properties:

Default Public ReadOnly Property Item(ByVal Key As String) As Object

and

Default Public ReadOnly Property Item(ByVal Index As Integer) As Object

When I try to use an object of this class in a COM only environment - like MS Word - there only one Item can be seen, and allways the first. So using the order above I can query collection items only by Key, when I change the order I can query only by Index.
This problem does not occour under .NET.

My question is: how to do VB.NET overriding, polymorphism to satisfy COM requirements?

(K)

(K)

Re: COM & VB.NET overloading

Heath Stewart5-Jan-04 13:41

Heath Stewart

5-Jan-04 13:41

Because overloading isn't supported in COM, hence a COM-Callable Wrapper (CCW) can't be created properly. Choose one or the other, but not both.

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Re: COM & VB.NET overloading

Jörgen Sigvardsson6-Jan-04 6:12