Howto pass COM object as param in event

[Jean-Guy2000]

How do you instance a new COM object and pass it as a parameter in an event. For example...

// Event declare in IDL
[id(1), helpstring("method GotServer")] HRESULT GotServer(IServerInfo** pServer);

// ------------- My code to attempt to instance a ServerInfo object and fire and event passing it ------------

CComPtr< IServerInfo > pNewServer;
HRESULT hr = pNewServer.CoCreateInstance(__uuidof(ServerInfo));
if(SUCCEEDED(hr))
{
      // Populate COM object properties here.....
      // Now Fire Event.
      Fire_GotServer(pNewServer);   <- This doesn't work.
}

Error message

error C2664: 'Fire_GotServer' : cannot convert parameter 1 from 'class ATL::CComPtr<struct IServerInfo>' to 'struct IServerInfo ** '

[[email protected]]

Hi,

IServerInfo* pNewServer = NULL;
HRESULT hr = pNewServer->CoCreateInstance(__uuidof(ServerInfo));
if(SUCCEEDED(hr))
{
	 // Populate COM object properties here.....
	 // Now Fire Event.
	 Fire_GotServer( &pNewServer );
}

Do you need an IServerInfo** ? I would expect you to need the double indirection if you were going to instantiate in the method. Does IServerInfo have mutators and accessors?

[Jean-Guy2000]

I don't know.. I am new to COM, I know how to pass it as a return item in a method but not in an event.


I tried your code and get this..

error C2039: 'CoCreateInstance' : is not a member of 'IServerInfo'

[Siddhartha]

You are almost there... See the methods parameters... It takes a pointer to an interface pointer.

CComPtr< IServerInfo > pNewServer;
HRESULT hr = pNewServer.CoCreateInstance(__uuidof(ServerInfo));
if(SUCCEEDED(hr))
{
	  // Populate COM object properties here.....
	  // Now Fire Event.
	  Fire_GotServer(&pNewServer);
}

[Jean-Guy2000]

Almost there, The code compiles now... but when I

Fire_GotServer( &pNewServer );

I get a crash here....

T** operator&()
{
ATLASSERT(p==NULL); <----- Debugger stops here.
return &p;
}
_NoAddRefReleaseOnCComPtr<T>* operator->() const

------ Callstack ----

ATL::CComPtr<IServerInfo>:perator&() line 469 + 40 bytes
CGuiClient::OnGotServer(ServerData * 0x02ac43d0) line 118 + 8 bytes <- call Fire_ method here...


thanks for the help.

[Siddhartha]

Actually... You need to review the purpose.

You get the ASSERT because the pointer is NOT NULL (It is valid).

Is the purpose of Fire_GotServer to return a valid pointer to the caller as [out, retval] seems to imply? Then, you should not be creating an instance of it.

If the purpose of Fire_GotServer is NOT to return a valid pointer rather to accept one, then the signature should be simply [in], and the method should accept merely a pointer and not a pointer to a pointer.

[Jean-Guy2000]

I want to raise an event (in Vb application) and pass a populated COM object to it. This is so I don't have to pass 9 diffrent short/string parameters.

I am new to COM so I don't understand exactly what I am doing, just looking at example code and replicating it in hopes of getting what I want.

I need know how to create an instance of the com object, populate it and fire the event passing this newly contrusted object (with it's 9 properties populated) back to Visual Basic application.

[Siddhartha]

I am new to COM so I don't understand exactly what I am doing, just looking at example code and replicating it in hopes of getting what I want.

Well... Even if you are replicating example code... Do so after understanding what it does.

Simply copy-pasting will not help you, and mostly harass the developer who has to fix bugs in your code long after.

I need know how to create an instance of the com object, populate it and fire the event passing this newly contrusted object (with it's 9 properties populated) back to Visual Basic application.

This is a pretty simple requirement, and needs you to pass an object and not get one - therefore, basic C++ tells that you don't need to pass a pointer to the object, rather the object (IServerInfo*) itself.

You are almost there. You don't need a double pointer.

Your IDL definition should be -

[id(1), helpstring("method GotServer")] HRESULT GotServer([in] IServerInfo* pServer);

Change your method's signature appropriately.

The usage should be...

CComPtr< IServerInfo > pNewServer;
HRESULT hr = pNewServer.CoCreateInstance(__uuidof(ServerInfo));
if(SUCCEEDED(hr))
{
	  // Populate COM object properties here.....
	  // Now Fire Event.
	  Fire_GotServer (pNewServer); 
}

[Jean-Guy2000]

Thanks that worked perfectly

[Siddhartha]

You are welcome...