Re: Inheritance and MFC

"Nobody" <>
Tue, 3 Jul 2007 17:30:28 -0700
Hi Joe,

Why is a grid object not derived from CWnd in the first place?

I wanted to make the grid object independent of MFC.
The only reason I am using CObject is for Serialization.
I am using the registry and a few other MFC functions, OnDraw(), =
OnMouseMove(), etc.
I should actually make several layers, but it is what it is for now.

I noticed that the more I use the grid object, the more I have to keep =
adding scroll bars for pan, zoom, etc.
So, my idea was to make a CWnd GridSB Class that implements Scrollbars.
That class inherits from the Grid CObject class.
Then, I can leave the scroll bars inside of the CGrid Object, instead of =
Creating scroll bars each time.

This is basically what I have.

CGrid : public CObject

CGridSB: public CGrid, public CWnd
    CScrollbar sb;
    SetScreenRect(){ Position Scrollbars(); }

    CGridSB sb;

"Joseph M. Newcomer" <> wrote in message =

Multiple inheritance is chancy in MFC. At least one rule is the CWnd =

class must be the

first class. But in this case, I don't see how a visible object like =

a grid could *not*

derive directly from CWnd, and since CWnd derives from CObject, there =

is no need for the

inheritance from CObject in the first place.
Why is a grid object not derived from CWnd in the first place?
On Tue, 3 Jul 2007 02:49:21 -0700, "Nobody" <> wrote:


I have a grid object. The Grid Object inherits from CObject.
There are no controls and I was thinking about adding some. Zoom, Pan, =


So, I have extantiated a new class that inherits from CGrid and CWnd.
class CGridSB : public CGrid, public CWnd

Now, I would like to add some controls to the Grid Object.
The problem is that the controls needs an m_hWnd
I am not sure what to do?


_AFXWIN_INLINE void CScrollBar::ShowScrollBar(BOOL bShow)
{ ASSERT(::IsWindow(m_hWnd)); ::ShowScrollBar(m_hWnd, SB_CTL, bShow); =


I understand that the CGridSB oject needs to handle the Scrollbar =

messages, so I need a message map

and perphaps a DECLARE_DYNCREATE along with an IMPLEMENT_DYNCREATE =


I just need to get past the m_hWnd error.

Thanks for your help,

Joseph M. Newcomer [MVP]
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