I have a lot of CDialogEx derived classes that do something like this in OnInitDialog:

CMeetingScheduleAssistantApp::InitialiseResizeIcon(m_bmpResize, m_lblResize, this);
CMeetingScheduleAssistantApp::RestoreWindowPosition(_T("PublisherDB"), this, true);

Then, I have the following added to each derived dialog class:

int CPublishersDatabaseDlg::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CDialogEx::OnCreate(lpCreateStruct) == -1)
        return -1;

    // Save Initial window size to m_rcInit
    GetWindowRect(&m_rcInit);

    return 0;
}

void CPublishersDatabaseDlg::OnGetMinMaxInfo(MINMAXINFO* lpMMI)
{
    // Set the minimum window size to initial size.
    lpMMI->ptMinTrackSize.x = m_rcInit.Width();
    lpMMI->ptMinTrackSize.y = m_rcInit.Height();

    CDialogEx::OnGetMinMaxInfo(lpMMI);
}

void CPublishersDatabaseDlg::OnClose()
{
    CMeetingScheduleAssistantApp::SaveWindowPosition(_T("PublisherDB"), this);
    CDialogEx::OnClose();
}

The only thing that is different for each dialog is the phrase that is used for saving the window position.

I want to have a based CDialogEx class that I can inherit from that will perform the above actions. I have looked on SO and seem some questions and creating a CDialog class and inheriting from another CDialog class. But this class I want to create is more generic. Effectively to be used as a base instead of CDialogEx.

Can this be done? Am I over-complicating this?

Problems

Why I try to create a new class, derived from CDialogEx:

I don't know if it is because it requires a dialog ID as stated here.

Classes such as CDialog, CFormView, or CPropertyPage, which require a dialog ID.

So I can't work out the correct way to create a base CDialogEx class for use in all my other dialog classes.

Update

I created this code and it tells me that CResizingDialog is not a class or a namespace:

#include "ResizingDialog.h"
#include "resource.h"
#include "stdafx.h"

IMPLEMENT_DYNAMIC(CResizingDialog, CDialogEx)

CResizingDialog::CResizingDialog(const CString& strWindowID, UINT nIDTemplate, CWnd* pParent = nullptr)
    : m_strWindowID(strWindowID), CDialogEx(nIDTemplate, pParent)
{

}

CResizingDialog::~CResizingDialog()
{
}

void CResizingDialog::DoDataExchange(CDataExchange* pDX)
{
    CDialogEx::DoDataExchange(pDX);
}

BEGIN_MESSAGE_MAP(CResizingDialog, CDialogEx)
    ON_WM_CREATE()
    ON_WM_GETMINMAXINFO()
    ON_WM_CLOSE()
END_MESSAGE_MAP()


int CResizingDialog::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CDialogEx::OnCreate(lpCreateStruct) == -1)
        return -1;

    // Save Initial window size to m_rcInit
    GetWindowRect(&m_rcInit);

    return 0;
}


void CResizingDialog::OnGetMinMaxInfo(MINMAXINFO* lpMMI)
{
    // Set the minimum window size to initial size.
    lpMMI->ptMinTrackSize.x = m_rcInit.Width();
    lpMMI->ptMinTrackSize.y = m_rcInit.Height();

    CDialogEx::OnGetMinMaxInfo(lpMMI);
}


void CResizingDialog::OnClose()
{
    SaveWindowPosition(m_strWindowID, this);

    CDialogEx::OnClose();
}

Based on the comments encouraging me to try to create the class manually, I have it working:

#include "stdafx.h"
#include "resource.h"
#include "ResizingDialog.h"

IMPLEMENT_DYNAMIC(CResizingDialog, CDialogEx)

CResizingDialog::CResizingDialog(const CString& strWindowID, UINT nIDTemplate, CWnd* pParent /* nullptr */, bool bOnlyStorePosition /* false */)
    : m_strWindowID(strWindowID),
      m_bOnlyStorePosition(bOnlyStorePosition), CDialogEx(nIDTemplate, pParent)
{

}

CResizingDialog::~CResizingDialog()
{
}

void CResizingDialog::DoDataExchange(CDataExchange* pDX)
{
    CDialogEx::DoDataExchange(pDX);
}

BEGIN_MESSAGE_MAP(CResizingDialog, CDialogEx)
    ON_WM_CREATE()
    ON_WM_GETMINMAXINFO()
    ON_WM_CLOSE()
END_MESSAGE_MAP()

int CResizingDialog::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
    if (CDialogEx::OnCreate(lpCreateStruct) == -1)
        return -1;

    // Save Initial window size to m_rcInit
    GetWindowRect(&m_rcInit);

    return 0;
}

void CResizingDialog::OnGetMinMaxInfo(MINMAXINFO* lpMMI)
{
    // Set the minimum window size to initial size.
    lpMMI->ptMinTrackSize.x = m_rcInit.Width();
    lpMMI->ptMinTrackSize.y = m_rcInit.Height();

    CDialogEx::OnGetMinMaxInfo(lpMMI);
}

void CResizingDialog::OnClose()
{
    SaveWindowPosition(m_strWindowID, this);

    CDialogEx::OnClose();
}

void CResizingDialog::OnOK()
{
    SaveWindowPosition();
    CDialogEx::OnOK();
}

BOOL CResizingDialog::OnInitDialog()
{
    CDialogEx::OnInitDialog();

    if(!m_bOnlyStorePosition)
        InitialiseResizeIcon(m_bmpResize, m_lblResize, this);

    RestoreWindowPosition(m_strWindowID, this, true);

    return TRUE;  // return TRUE unless you set the focus to a control
                  // EXCEPTION: OCX Property Pages should return FALSE
}

I decided to duplicate the methods that were in the app class into this new dialog class instead. Eventually they can be removed from the app class. The only thing I also had to do was #include my resource file because the image needs to know the value of the resource ID.

This is the ResizingDialog.h header:

#pragma once
#include <afxwin.h>

class CResizingDialog : public CDialogEx
{
    DECLARE_DYNAMIC(CResizingDialog)

public:
    CResizingDialog(const CString& phrase, UINT nIDTemplate, CWnd* pParent = nullptr, bool bOnlyStorePosition = false); // Constructor
    virtual ~CResizingDialog(); // Destructor

protected:
    void OnOK() override;
    virtual void DoDataExchange(CDataExchange* pDX) override;    // DDX/DDV support
    void SaveWindowPosition(void) { SaveWindowPosition(m_strWindowID, this); }

public:
    BOOL OnInitDialog() override;
    afx_msg int OnCreate(LPCREATESTRUCT lpCreateStruct);
    afx_msg void OnGetMinMaxInfo(MINMAXINFO* lpMMI);
    afx_msg void OnClose();
    DECLARE_MESSAGE_MAP()

private:
    CBitmap m_bmpResize;
    CStatic m_lblResize;
    CRect m_rcInit;
    CString m_strWindowID;
    bool m_bOnlyStorePosition;

    void RestoreWindowPosition(CString strWindow, CWnd* pWindow, bool bOverrideState = false);
    void SaveWindowPosition(CString strWindow, CWnd* pWindow);
    void InitialiseResizeIcon(CBitmap& rBmpResize, CStatic& rLblResize, CWnd* pDialog);
};

The actual functions SaveWindowPosition, RestoreWindowPosition and InitialiseResizeIcon are not shown here as they don't directly relate to the issue.