Benefits of Protected Construtors in MFC

From:

=?Utf-8?B?c2F3ZXI=?= <sawer@discussions.microsoft.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 22 May 2008 03:16:01 -0700

Message-ID:

<AF2D44D0-5F17-404E-88A3-94F1894B867E@microsoft.com>

Hi

I want to ask you about logic behind the protected constructors in MFC.
Firstly i want to give an example. This make easier to explain the problem.

I added a class which is driven from CView class. And i want to show it when
clicked "View->New Window" menu.
***********************
#pragma once

// code view

class code : public CView
{
    DECLARE_DYNCREATE(code)

protected:
    code(); // protected constructor used by dynamic creation
    virtual ~code();

public:
    virtual void OnDraw(CDC* pDC); // overridden to draw this view
#ifdef _DEBUG
    virtual void AssertValid() const;
#ifndef _WIN32_WCE
    virtual void Dump(CDumpContext& dc) const;
#endif
#endif

protected:
    DECLARE_MESSAGE_MAP()
};
*************************

I can not call like this:
CView* pView = (CView*) new code; // error C2248 cannot access protected
member

1-) Why are the wizard declare classes constructors protected or private?
What is the benefit/logic? For example If i add class which is derived from
CEdit with wizard, its constructors is declared public but if it is derived
from CEditView its constructor is declared protected. Why is that so?

2-)Is changing protected to public best way?

3-) Where must i handle the menu selection, i mean creating new form. In
MainFrm.cpp or something else?

If you help me to understand this concept i will be very glad