Re: _variant_t Question - COM Discussion Boards

7-Dec-06 22:48

Hi All,

Description of Problem:-

I have a interface pointer to some custom dual interface. I am creating a object of _variant_t class like "_variant_t vtSample(pICustom);".

vtSample is created and assigned value as 'TRUE' and its vt as VT_BOOL.
It should have been VT_DISPATCH instead of VT_BOOL and value as some memory address.

Can anyone explain the above behavior?

Thanks...

Suraj Gupta

prasad_som7-Dec-06 23:02

7-Dec-06 23:02

Can you show some code ?

Gupta Suraj wrote:
I am creating a object of _variant_t class like "_variant_t vtSample(pICustom);".

vtSample is created and assigned value as 'TRUE' and its vt as VT_BOOL.

Why you are assigning its vt as VT_BOOL.

Gupta Suraj wrote:
It should have been VT_DISPATCH instead of VT_BOOL and value as some memory address.

Can anyone explain the above behavior?

I'm confused here to understand your problem. Can you explain in detail.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj7-Dec-06 23:26

7-Dec-06 23:26

Hi Prasad,

Thanks for the reply...

I am not explicitly assigning vt to VT_BOOL.

"_variant_t vtSample(pICustom);"

The above statement is causing vtSample object to be instantiated and initialized with vt= VT_BOOL and its value as 'TRUE'.

As pICustom is dual interface pointer so value of vtSample should be pointer to v-table and its vt should be VT_DISPATCH not VT_BOOL.

I don't know why it so?

Am I able to make you understand the problem?

Thanks...

Suraj Gupta

prasad_som8-Dec-06 1:49

8-Dec-06 1:49

Gupta Suraj wrote:
"_variant_t vtSample(pICustom);"

Can you show code snippet, how you are using this interface? There is no way it should assign vt as VT_BOOL , unless pICustom is BOOL.
While debugging, you can step through the contructor of _variant_t , see which contructor is been called.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj8-Dec-06 3:26

8-Dec-06 3:26

Thanks Prasad...

Actually,pICustom is a smart pointer. So when "vtSample(pICustom)" is executed, bool operator of _com_ptr template class is called. What I think is that the best matching constructor of _variant_t class is that which takes a bool as its paramter.So first bool operator of _com_ptr is called to convert the parameter to bool.

We don't have a overloaded constructor of _variant_t class which takes smart pointer as its parameter.

Please send your comment on this. Am i thinking in right direction?

Suraj.

Suraj Gupta

Ed Gadziemski8-Dec-06 18:29

Ed Gadziemski

8-Dec-06 18:29

Try explicitly casting your object to an IDispatch pointer, for example (IDispatch *)pICustom. That should eliminate falling through to bool.

Gupta Suraj10-Dec-06 17:44

10-Dec-06 17:44

Thanks...It worked...

Suraj Gupta

prasad_som10-Dec-06 21:29

10-Dec-06 21:29

Though, you had a solution to your problem;

Gupta Suraj wrote:
bool operator of _com_ptr template class is called.

Which operator bool you are talking about ? In fact, it should return you custom interface type.
Its implementated like this,

operator T*()   {
    return p;

So I feel, it should return interface pointer.
Can you show how you have declared this interface ?

Gupta Suraj wrote:
We don't have a overloaded constructor of _variant_t class which takes smart pointer as its parameter.

No, CComPtr, will be called for operator T*. Which returns appropriate interface pointer.
i.e. consider this declaration,

CComPtr<IMyInterface> pMy;
_variant_t f(pMy);

Here,in second statement pMy->Operator T* will be get called first. Which returns IMyInterface*.
So, it will set for VT_IDISPATCH automatically.
You dont even need to cast it.

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj11-Dec-06 18:28

11-Dec-06 18:28

Hi Prasad,

Here is code snippet of my application..

// Smart pointer(SampleObjects::ISampleSetDualPtr) typedef declarations
_COM_SMARTPTR_TYPEDEF(ISampleSetDual, __uuidof(ISampleSetDual));
// Smart pointer typedef declarations

SampleObjects::ISampleSetDualPtr pMutipleValues = SampleObjects::ISampleSetDualPtr )propertyPtr->Value;

_variant_t vtMultiValue(pMutipleValues);//This statement first causes bool operator of template class _com_ptr_t being called and then overloaded constructor of _variant_t class being called which takes bool as input parameter.

template<typename _iiid=""> class _com_ptr_t
{
......
......
......
operator bool() const throw()
{
return m_pInterface != NULL;
}
}

Please let me know your input on this.

Thanks,
Suraj

Suraj Gupta

prasad_som11-Dec-06 19:22

11-Dec-06 19:22

Now I got your point.
I was in assumption, you are using CComPtr, where as you are using _com_ptr_t . Both are having different implementations.

Gupta Suraj wrote:
_variant_t vtMultiValue(pMutipleValues);//This statement first causes bool operator of template class _com_ptr_t being called and then overloaded constructor of _variant_t class being called which takes bool as input parameter

Here, compiler looks for mathcing constructor of _variant_t. It doesn't find one with given smart pointer. _com_ptr_t is overloaded for operator bool(). Hence, there is match betn constructor with bool parameter of _variant_t and passed smart pointer variable.

Type casting as said in one of previous replies is one solution.
Or you can Use

_variant_t vtMultiValue(pMutipleValues.GetInterfacePtr());//

to resolve ambiguity .

Prasad
Notifier using ATL | Operator new[],delete[][^]

Gupta Suraj11-Dec-06 19:36

11-Dec-06 19:36

Thank you...

Solution you suggested works.

I thought another solution that works in this case is

_variant_t vtMultiValue(pMutipleValues, true);

You have being a great help.
Suraj

Suraj Gupta

prasad_som11-Dec-06 19:51

Automation, cross thread problem

11-Dec-06 19:51

Gupta Suraj wrote:
_variant_t vtMultiValue(pMutipleValues, true);

Yes, that's becuase, as in previous case compiler was picking _variant_t( bool bSrc ) throw( ) version of constructor as match.

But, in this case that wont happen because of extra parameter provided(That resolved ambuguity in one way).
And compiler matches this construcor _variant_t( IDispatch* pDispSrc, bool fAddRef = true ) throw( ); To do that match, first parameter is typecasted with IDispatch*.

Prasad
Notifier using ATL | Operator new[],delete[][^]

anderslundsgard6-Dec-06 21:36

anderslundsgard

6-Dec-06 21:36

I’m automating MS Project and when I listen on an event from MS Project all works fine but when I’m trying to fill a TreeView I got the following exception:

Action being performed on this control is being called from the wrong thread. Marshal to the correct thread using Control.Invoke or Control.BeginInvoke to perform this action.

What have I missed?

_____________________________

...and justice for all

APe

«_Superman_»6-Dec-06 22:50

«_Superman_»

6-Dec-06 22:50

I'm guessing you got the TreeView control from one thread and are filling from another.

« Superman »

Roger Stoltz6-Dec-06 22:50

Roger Stoltz

6-Dec-06 22:50

Interfaces that cross apartment boundaries has to be marshaled.
No surprises here, it's according to the COM spec.

When you spawn a thread that should use COM stuff, you create another apartment and you have to initalize COM for that apartment with a call to ::CoInitalize() or ::CoInitializeEx(). If you want to use a COM interface that you got in another thread you have to marshal that interface to the new apartment.
There are several ways of doing this, but I think in your case the easiest way would be to use ::CoMarshalInterThreadInterfaceInStream() and ::CoGetInterfaceAndReleaseStream().
Have a look at MSDN here[^].

--
Roger

"It's supposed to be hard, otherwise anybody could do it!" - selfquote

"No one remembers a coward!" - Jan Elfström 1998
"...but everyone remembers an idiot!" - my lawyer 2005 when heard of Jan's saying above

lafleon7-Dec-06 10:25

lafleon

7-Dec-06 10:25

Hello,

.NET interop service marshals all interfaces automatically for all new threads. Marshaling fails for incorrect data types in the interface. You can only use automation supported data types like BSTR, VARIANT_BOOL, SAFEARRAY etc. For complete list of data types see VS documentation on MSDN or ATL wizard in Visual Studio.

Regards

anderslundsgard7-Dec-06 2:40

anderslundsgard

7-Dec-06 2:40

Ok, I've seen that function before.

I programming in .NET (C#). What type of method can I use in .NET.

I've run into the Control.Invoke method but I have about 30 calls to my TreeView and it is very time-consuming to rewrite all these calls...

_____________________________

...and justice for all

APe

Roger Stoltz7-Dec-06 3:22

Roger Stoltz

7-Dec-06 3:22

d00_ape wrote:
I programming in .NET (C#). What type of method can I use in .NET.

Sorry, I neither do .NET nor C#.

d00_ape wrote:
I've run into the Control.Invoke method but I have about 30 calls to my TreeView and it is very time-consuming to rewrite all these calls...

Why would all those calls have to be rewritten?
This cannot have anything to do with eventual calls to the marshalling API.

--
Roger

anderslundsgard7-Dec-06 4:01

anderslundsgard

7-Dec-06 4:01

Roger Stoltz wrote:
This cannot have anything to do with eventual calls to the marshalling API

Sorry I don't know what you mean with that...

I've posted this topic in the C# forum.

_____________________________

...and justice for all

APe