How to execute methods from ATL/COM base class

[Doug Knudson]

In VS6 C++, I have a windowless ATL control. To get a Device Context from the container, I belive I need to execute the GetDC() method of one of the base classes for the control, specifically IOleInPlaceObjectWindowless. I tried to do this: CDC *pDC = IOleInPlaceObjectWindowless::GetDC(); But it doesn't work so I am at a loss as to how to execute a method on the IOleInPlaceObjectWindowless interface. Any help would be greatly appreciated, Thanks, Doug

Doug Knudson

[prasad_som]

You can use methods exposed by interfaces ,only. Or you want to say smething else ?

[Doug Knudson]

Thanks for the reply. I didn't ask my question very well, but basically I am writing a windowless ATL component and need the Device Context from the Parent/Container so that I may draw in event handlers (for example, in MouseMove()). During my length time searching, all I could find was people saying that I needed to just execute the GetDC() method of the IOleInPlaceObjectWindowless interface like this:

HDC hDC = NULL;
HRESULT hr = IOleInPlaceObjectWindowless::GetDC(myRect,myFlags,&hDC);

The compiler interprets the above as trying to execute a static member function, which, of course, GetDC() isn't. If I just use:

GetDC();

I get the API GetDC() that expects there to be a m_hWnd, which there isn't (windowless control), so I am pretty lost as to how to do this. Thanks, Doug

Doug Knudson

[Mike Dimmick]

There is no GetDC method on the IOleInPlaceObjectWindowless interface, nor any of its base interfaces. You should generally be doing all your drawing in your implementation of IViewObject::Draw, i.e. in OnDraw. If you need to do some drawing outside of this, the GetDC call is on IOleInPlace_Site_Windowless, which you have to ask the container for. I believe you should call InternalGetSite (which is inherited from CComControlBase) to retrieve a pointer to this interface.

"Multithreading is just one damn thing after, before, or simultaneous with another." - Andrei Alexandrescu

[Doug Knudson]

Hi Mike, Thanks! I will give that a try. I am doing the bulk of my drawing in OnDraw() but I need to drag a selection rectangle during the MouseDown, MouseMove, MouseUp events so I need to (or at least I think I need to :)) have the DC outside of what is handed to me in OnDraw() ?? Thanks again, Doug

Doug Knudson