Re: Inheritance and MFC

Hi Joe,

Presumably there is not a single line of code in CGrid that uses any feature of MFC
whatsoever, right?
That is the plan. Who knows whether it will work or not, but just for arguments sake, let's just say that it does.

If this is so, then it has no display mechanism, no way to interact with the mouse, no way
to display anything in a window, etc. It would be what we think of as a "document".
Nothing wrong with that.
This is my plan.

So what you would do is create a "view" on this object. The "view" would provide the
display and user interaction components.
That is a big correct-a-mundo.

There would be no reason to use serialization at all; anything that would be in a grid
should be easily serializable using simple I/O mechanisms, to write integers, floats, and
strings. So CObject buys nothing.
I didn't see a need to inherit from CWnd, since all I needed was Serialization.
(Is there no apparent reason to ever inherit from CObject as opposed to CWnd? or am I completely mistaken?)
I suppose I could have used CFile or something similar, but I am just messing around. Familiarizing myself with the interworkings of MFC.
Like I said. It is not complete.
All I want to do is add Scrollbars to the object.
Just trying to keep it seperate.

But if you DO make it a CObject, it is STILL a "document", with no display, drawing, or
windowing capabilities
That is my plan.

Think of a separation of data and display, at it becomes obvious that your CGrid would
most likely be contained in a CDocument class in MFC, and all drawing and interactions
would be in a CView, or a class which is embedded in a CView.
That is what I am thinking of, but a bit differently.
There is no Document, but there are variable that are stored via registry or disk.

I wanted the base class to just inherit from CObject, becuase that is all it needed, just to store to disk
Now, I am adding Scrollbars to the object, therefore it needs more than just CObject.
I guess I will have to change CGrid to inherit from CWnd and add the CScrollbars to the base class, since I can't
inherit from CObject twice.

All in all, is there never a need to inherit from CObject as oppposed to CWnd?
Since, everthing in MFC will be in a View and everything in a View needs needs CWnd.
What is the purpose of ever inheriting from CObject?
Should I just inherit from CWnd and never inherit from CObject?
What the heck is the purpose of CObject? An unused Reference? Like PURE in the dialog resource?

Thanks,
"Joseph M. Newcomer" <newcomer@xxxxxxxxxxxx> wrote in message news:6tjm83h4t0oqhkb6d0i0fcj2e5lqmrtv8a@xxxxxxxxxx
Presumably there is not a single line of code in CGrid that uses any feature of MFC
whatsoever, right?

If this is so, then it has no display mechanism, no way to interact with the mouse, no way
to display anything in a window, etc. It would be what we think of as a "document".

Nothing wrong with that.

So what you would do is create a "view" on this object. The "view" would provide the
display and user interaction components.

There would be no reason to use serialization at all; anything that would be in a grid
should be easily serializable using simple I/O mechanisms, to write integers, floats, and
strings. So CObject buys nothing.

Therefore, there is no need to encapsulate a grid in a CObject as such.

But if you DO make it a CObject, it is STILL a "document", with no display, drawing, or
windowing capabilities, so now you need to create a grid-view, and that would be derived
from CWnd, so it would not need to be derived from the grid; I think you are confusing
display and data, representation and manipulation, and the confusion has led you down a
design path which is apparently confusing to you, and it should be, because it is probably
wrong. When a design starts exhibiting these problems, you should reconsider the design.

Think of a separation of data and display, at it becomes obvious that your CGrid would
most likely be contained in a CDocument class in MFC, and all drawing and interactions
would be in a CView, or a class which is embedded in a CView.
joe
On Tue, 3 Jul 2007 22:55:56 -0700, "Nobody" <Nobody@xxxxxxxxx> wrote:

Hi Joe,

Well, if you made it a CObject, it is most definitely *not* independent of MFC! And the
concept of including it in an MFC class seems more than a little strange.

In fact, the "using ... a few other MFC functions" means you are already committed to MFC.

Yes, and No.
Yes, I have committed to using MFC, because that is what I am developing the project with.
No, because it is able to be used independent of MFC. (At least that is what I was trying to do.)

Yeah, your right, I need to clean it up somewhat to conform to do what I want, but I was holding that off for now.

I am a bit confused about segragating the class into independent "Seperately indentifiable" objects. Hence the post.
CGrid - Independent
CGridMFC - MFC Dependent - Only Serialization. (Does not need CWnd.)
CGridSB - MFC Dependent plus Scrollbars.

I suppose like David said, I can't go that route and I will have to just inherit from CWnd in the base class or the CGridMFC class.

Thanks anyways,
"Joseph M. Newcomer" <newcomer@xxxxxxxxxxxx> wrote in message news:dc9m83dkbfgjg9gkj8itlkcrc33mhou1q7@xxxxxxxxxx
Well, if you made it a CObject, it is most definitely *not* independent of MFC! And the
concept of including it in an MFC class seems more than a little strange.

In fact, the "using ... a few other MFC functions" means you are already committed to MFC.
joe

On Tue, 3 Jul 2007 17:30:28 -0700, "Nobody" <Nobody@xxxxxxxxx> wrote:

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;
CreateScrollbars();
SetScreenRect(){ Position Scrollbars(); }
}

CView::OnDraw()
{
CGridSB sb;
sb.SetScreenRect(Rect);
sb.OnDraw(pDC);
}

Regards,
"Joseph M. Newcomer" <newcomer@xxxxxxxxxxxx> wrote in message news:hndk83t2i52oo7o21fhrt0jpj8f5vn97u7@xxxxxxxxxx
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?
joe
On Tue, 3 Jul 2007 02:49:21 -0700, "Nobody" <Nobody@xxxxxxxxx> wrote:

Hi,

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

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?

VERIFY(c_sbHZoom.Create(
SBS_VERT | SBS_RIGHTALIGN | WS_CHILD |WS_BORDER,
Rect,
this,
1234)
);

_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 member.

I just need to get past the m_hWnd error.

Thanks for your help,
Joseph M. Newcomer [MVP]
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
Joseph M. Newcomer [MVP]
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
Joseph M. Newcomer [MVP]
email: newcomer@xxxxxxxxxxxx
Web: http://www.flounder.com
MVP Tips: http://www.flounder.com/mvp_tips.htm
.

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