How can I create a COM hook like DrCOM Monitor? - COM Discussion Boards

23-Feb-04 2:18

QueryInterface is a discovery mechanism. Let's say you have an interface (any interface, it doesn't matter) to a COM component. You can, using a method in the interface, ask the component if it supports another interface that you know about.

For instance, you might have an IFrooble interface on an object, and you want to know if it supports automation using the 'classic IDispatch' method.

You say something like:

HRESULT hr;
IDispatch* pDisp = NULL;
hr = pFrooble->QueryInterface( IID_IDispatch, reinterpret_cast<void**>(&pDisp));

if (SUCCEEDED(hr))
{
// Yep, it does dispatch, and we now have that interface as well
// as the IFrooble one.
}
else
{
// No, it doesn't or can't provide that interface
}

Does that help?

Another scenario is versioned interfaces, where a client will ask for successive interfaces (eg IFooBar4, IFooBar3, IFooBar2, IFooBar) until it gets one it's happy with.

Steve S

Re: queryInterface

Big_M24-Feb-04 1:24

Big_M

24-Feb-04 1:24

If you look from the C++ point of view,

All you interfaces to COM object are abstract base classes with pure virtual functions. And your COM object gives implementation of all these functions.

So when you call QueryInterface, it simple casts the COM object(this) into the interface pointer, increase a reference count and return that pointer. This way you can only call the functions declared in that interface.

COM DLL

waliop23-Feb-04 0:55

waliop

23-Feb-04 0:55

Wt diffrence between simple dll and COM dll? Confused | :confused:

sdfsdfsdfhsdfh

Re: COM DLL

Steve S23-Feb-04 2:11

How can I create a COM hook like DrCOM Monitor?

23-Feb-04 2:11

[fx: deep breath]
a COM dll will provide code for registration/deregistration, as well as a mechanism to create lifetime-managed components. In general, it provides a published binary interface (which should be immutable) to allow use of the component(s) in languages other than the one it was written in.
It follows a standard mechanism for requesting component creation, and includes mechanisms for lifetime management (IUnknown::AddRef, IUnknown::Release) as well as a mechanism for capability discovery (IUnknown::QueryInterface) which is extensible.

(Guys, did I miss anything?)

Steve S

kenokabe22-Feb-04 21:05

kenokabe

22-Feb-04 21:05

DrCOM Monitor
http://www.ddevel.com/DrCOM/DrCOMMonitor.asp

I'm trying to externally control a target app that is built on COM.

I have read
http://www.codeproject.com/com/automatingwindowsapps.asp

However, this technique looks way too comlicated in my case to realize what I'd like to do, and in fact, looking at the DrCOM folder at least, it seems simpler than the preject above.

Using DrCOM, the whole COM analyzed by the tool is marked as 'Automated', and I actually could 'Invoke' the API function from DrCOM, such as 'Object.SendLogout()' which actually made the target app. behave that way. The target application received the message from the external tool, and was controled right way. Wonderful, I felt.

What I'd like to do is to 'Invoke' the command of COM that is the server of the target application from the external application that I will code in C#.

I posted on C# board, too.

Any comment? Thank you very much in advance. Confused | :confused:

Best,
Ken

outlook embedding

emmatty21-Feb-04 23:13

emmatty

21-Feb-04 23:13

hello,
i am developing an addin for outlook to insert an image to outlook email body but my problem when i insert image on top of a text (using DOM) the text splits into two sides and image got placed between the text but this is not allowed i have to place image on top of the text without the splitting. Is there any way in VC++,COM,DHTML. Confused | :confused:

Outlook Addin

chakkaradeepcc19-Feb-04 23:56

chakkaradeepcc

19-Feb-04 23:56

hi all,

am developing a Outlook Addin in VC++,i have added a button to the Inspectors window and now i want to retrieve the from address and subject from the inspector window (the window which gets opened when we click the message in the inbox!).how will i do it?

with regards,
chakkaradeep.

BSTR * parameter

dzsigit19-Feb-04 0:26

19-Feb-04 0:26

How can i get back a string from a COM method call?
I use this dispatch params:
DISPPARAMS DispatchParams;
DispatchParams.cArgs=3;
DispatchParams.rgvarg = new VARIANTARG[3];
DispatchParams.rgvarg[0].vt = VT_BYREF|VT_BSTR;
DispatchParams.rgvarg[0].pbstrVal = &bstrDocId;
DispatchParams.rgvarg[1].vt = VT_BYREF|VT_I4;
DispatchParams.rgvarg[1].plVal = &llngFlags;
DispatchParams.rgvarg[2].vt = VT_I4;
DispatchParams.rgvarg[2].lVal = 0;
DispatchParams.rgdispidNamedArgs=NULL;
DispatchParams.cNamedArgs=0;
if the bstrDocId is a BSTR then the invoke returns No such interface supported, if i use CComBSTR then the invoke succeeds but the result is that the bstrDocId becomes NULL. I don't understand this, how can it be NULL if it is not a pointer? If i initialize the CComBSTR with an exact length then the invoke also returns the "Nos such interface supported" error.
If anybody knows how to get back a string i would be pleaseful to see it.

dzsigit

Steve S19-Feb-04 1:06

19-Feb-04 1:06

Looking at this, the signature for the method you're calling is:

HRESULT somename([in,out]BSTR* docID, [in,out]long* flags, long x)

Is this correct?

Steve S

dzsigit19-Feb-04 3:52

19-Feb-04 3:52

Yes

Vi219-Feb-04 18:58

Vi2

19-Feb-04 18:58

AFAIK, you're using the illegal order of the arguments for Invoke - it should be the REVERSED order.

MSDN: "The arguments are passed in the array rgvarg[ ], with the number of arguments passed in cArgs. The arguments in the array should be placed from last to first, so rgvarg[0] has the last argument and rgvarg[cArgs -1] has the first argument. The method or property may change the values of elements within the array rgvarg, but only if it has set the VT_BYREF flag. Otherwise, consider the elements as read-only."

So your called function looks like
HRESULT somename(long x, [in,out]long* flags, [in,out]BSTR* docID)
instead of your function
long SelectDoc([in, out] BSTR* tstrDocID, [in, out] long* tintFlags, [in] long tintWindow);

With best wishes,
Vita

Steve S19-Feb-04 22:50

19-Feb-04 22:50

Doh!
I should have spotted that too! I blame the painkillers.

Steve S
"Of all the things I've lost, I miss my mind the most"

dzsigit19-Feb-04 23:01

19-Feb-04 23:01

Thanks for your help, but it still doesn't work. I've tried with MFC and it throws the same error.
Here is the code, maybe you can see something in it.

HRESULT hr;
OLECHAR FAR* szMember = L"SelectDoc";
DISPID DispatchID;
IDispatch * pDispatch;
IUnknown * pUnknown;
long llngFlags=0;
BSTR bstrDocId=SysAllocStringLen((OLECHAR*)"xxx", 256);
long llngReturn;

DISPPARAMS DispatchParams;
DispatchParams.cArgs=3;
DispatchParams.rgvarg = new VARIANTARG[3];
DispatchParams.rgvarg[0].vt = VT_I4;
DispatchParams.rgvarg[0].lVal = 0;
DispatchParams.rgvarg[1].vt = VT_BYREF|VT_I4;
DispatchParams.rgvarg[1].plVal = &llngFlags;
DispatchParams.rgvarg[2].vt = VT_BYREF|VT_BSTR;
DispatchParams.rgvarg[2].pbstrVal = &bstrDocId;
DispatchParams.rgdispidNamedArgs=NULL;
DispatchParams.cNamedArgs=0;
CoInitialize(NULL);
CoCreateInstance(..)
pUnknown->QueryInterface(..)
pDispatch->GetIDsOfNames(..)

hr = pDispatch->Invoke(DispatchID, IID_NULL, LOCALE_USER_DEFAULT, DISPATCH_METHOD, &DispatchParams, (VARIANT*)&llngReturn, NULL, NULL);

MFC code

COleDispatchDriver disp;
COleException* e=new COleException();
IDispatch *pdisp;
DISPID dispid;
OLECHAR FAR* szMember[1];
HRESULT hresult;

disp.CreateDispatch(..)
static BYTE parms[] = VTS_PBSTR VTS_PI4 VTS_I4;
pdisp = disp.m_lpDispatch;
szMember[0] = L"SelectDoc";
pdisp->GetIDsOfNames(IID_NULL, szMember, 1, LOCALE_SYSTEM_DEFAULT , &dispid);
long llngReturn;
long llngFlags;
BSTR bstrDocId=SysAllocString(..);

disp.InvokeHelper(dispid, DISPATCH_METHOD, VT_I4,(void*)&llngReturn, parms,&bstrDocId , &llngFlags, (long)0);

dzsigit

Vi220-Feb-04 0:29

Vi2

20-Feb-04 0:29

dzsigit wrote:
long llngReturn;
...
hr = pDispatch->Invoke(..., &DispatchParams, (VARIANT*)&llngReturn, ...);
I think that it's a bad practice to make the ambiguous casting to avoid the compiler error.

In any case the E_NOINTERFACE can be a valid HRESULT which can mean that there is no such Document as you specify.

With best wishes,
Vita

dzsigit20-Feb-04 2:38

20-Feb-04 2:38

What kind of Document do you mean? I only want to call my function that is written in .Net.

My function's return type is long, how can i get back a long value if i don't cast it to VARIANT *? I've read a lot of articles and the return value was everywhere casted like that.

dzsigit

Steve S22-Feb-04 22:19

22-Feb-04 22:19

If your function's return type is long, then it isn't an HRESULT.
Conventionally, automation methods all return an HRESULT to indicate success or failure, and if there is a 'logical' return value, it can be indicated by using the [retval] attribute on the appropriate value.

What is the actual IDL/ODL code for your method please...

Steve S

dzsigit23-Feb-04 1:05

23-Feb-04 1:05

The IDL code

[id(0x6002001a)]
long SelectDoc(
[in, out] BSTR* tstrDocID,
[in, out] long* tintFlags,
[in] long tintWindow);

dzsigit

Steve S23-Feb-04 2:08

23-Feb-04 2:08

OK, next question. You have tstrDocID and tintFlags as [in,out]. Does that mean you could pass in both of these and pass back different ones and that's what your COMponent is expecting to deal with?

Typically, you would see this written as

[id(0x6002001a)]
HRESULT SelectDoc([in,out]BSTR* tstrDocID, [in,out]long* tintFlags, [in] long tintWindow, [out,retval]long* pResult);

This makes it easy to return failures, via an unsuccessful HRESULT (top bit set),
and a return value flagged in this way is accessible by conventional assignment in environments such as VB.

Steve S

dzsigit23-Feb-04 2:34