My first scrollbar

I have been reading Prosise's MFC book and am trying to get my first scrollbar working in a ruler application but have encountered a couple of problems. Firstly when the scrollbar is moved it snaps back to its original position although this only occurs in debug builds strangely. The second problme is that it doesnt redraw properly leaving the numbers out of place or not there at all :(

I'd appreciate it if someone could take a look at my code for me :)

Code:

---

//app.h

#ifndef APP_H
#define APP_H

#include <afxwin.h>

class RulerApp : public CWinApp
{
public:
        virtual BOOL InitInstance( );
};


class RulerWin :public CFrameWnd
{
public:
        RulerWin( );
        afx_msg void OnPaint( );
        afx_msg void OnSize( UINT nType, int cx, int cy );
        afx_msg void OnHScroll( UINT nSBCode, UINT nPos, CScrollBar* pScrollBar );

protected:
        DECLARE_MESSAGE_MAP( )

private:
        int horzScrollPos;
        int horzPageSize;
        int virtualWidth;

};

RulerApp app;



#endif

---

Code:

---

//app.cpp

#include "app.h"

BOOL RulerApp::InitInstance( )
{
        m_pMainWnd = new RulerWin( );
        m_pMainWnd->ShowWindow( m_nCmdShow );
        m_pMainWnd->UpdateWindow( );

        return TRUE;
}


BEGIN_MESSAGE_MAP( RulerWin, CFrameWnd )
        ON_WM_PAINT( )
        ON_WM_SIZE( )
        ON_WM_HSCROLL( )
END_MESSAGE_MAP( )


RulerWin::RulerWin( )
{
        Create( NULL, _T("A strange ruler..."), WS_OVERLAPPEDWINDOW | WS_HSCROLL );
        virtualWidth = 4000;
}


void RulerWin::OnPaint( )
{
        CPaintDC dc( this );

        dc.SetWindowOrg( horzScrollPos, 0 );                //added to to ake

        dc.SetMapMode( MM_LOMETRIC );

        CBrush yellowBrush;
        yellowBrush.CreateSolidBrush( RGB( 240, 240, 0 ) );

        CRect ruler( 200, -700, 5000, -1150 );        //+ve up, +ve right

        CBrush* oldBrush = dc.SelectObject( &yellowBrush );
        dc.Rectangle( &ruler );
        dc.SelectObject( oldBrush );

        dc.SetBkMode( TRANSPARENT );
        dc.SetTextAlign( TA_CENTER | TA_TOP );

        int i;
        for( i = 200; i <= 5000; i += 100 )
        {
                if( i != 200 )
                {
                        char cm[ 3 ];
                        itoa( (i-200)/100, cm, 10 );
                        dc.TextOut( _T( i ), -1050, cm );
                }

                dc.MoveTo( i, -1100 );
                dc.LineTo( i, -1150 );
        }
}


void RulerWin::OnSize( UINT nType, int cx, int cy )
{
        CFrameWnd::OnSize( nType, cx, cy );

        //ALL THE FOLLOWING STUFF SYNCRONISES THE THUMB SIZE AND WINDOW SIZE
        int horzScrollMax = 0;
        horzScrollPos = horzPageSize = 0;

        if( cx < virtualWidth )                //screenwidth < workspace width
        {
                horzScrollMax = virtualWidth - 1;        //max scroll pos set to just less than workspace size
                horzPageSize = cx;                //page size set to screen width
                horzScrollPos = min( horzScrollPos, virtualWidth - horzPageSize - 1 );
        }

        SCROLLINFO si;

        si.fMask = SIF_ALL;
        si.nMin = 0;
        si.nMax = horzScrollMax;
        si.nPos = horzScrollPos;
        si.nPage = horzPageSize;

        SetScrollInfo( SB_HORZ, &si, TRUE );

}


void RulerWin::OnHScroll( UINT nSBCode, UINT nPos, CScrollBar* pScrollBar )
{
        int delta;
        const int MOVEMENT = 10;

        switch( nSBCode )
        {
        case SB_LINELEFT:
                delta = -MOVEMENT;
                break;

        case SB_PAGELEFT:
                delta = -horzPageSize;
                break;

        case SB_LINERIGHT:
                delta = MOVEMENT;
                break;

        case SB_PAGERIGHT:
                delta = horzPageSize;
                break;

        case SB_THUMBTRACK:
                delta = (int)nPos - horzScrollPos;
                break;

        default:
                break;
        }

        int scrollPos = horzScrollPos + delta;
        int maxPos = virtualWidth - horzPageSize;

        if( scrollPos < 0 )
        {
                delta = -horzScrollPos;
        }
        else if( scrollPos > maxPos )
        {
                delta = maxPos - horzScrollPos;
        }

        if( delta != 0 )
        {
                horzScrollPos += delta;
                SetScrollPos( SB_HORZ, horzScrollPos, TRUE );
                ScrollWindow( -delta, 0 );
        }
}

---

tia

remembered my login now :)

Still need help with this one though, its really put me off programming for a while :(

You don't seem to clearing the painting area before writing your updated text to it.

Secondly, when pasting code containing colons and brackets, please tick the "Disable smilies in this post" - it makes your post more readable.

Dont think I'm being lazy, but what do you mean clear the painting area? Is there a CPaintDC function you had in mind?

ok I now put an Invalidate( ) call in before I call ScrollWindow( ). This solves part of the problem but causes the screen to flash, so I'm sure this isnt the proper solution.

The other part of the problem is the difference between the debug and release builds, whereby the debug build causes the scrollbar to snap back and the release build doesnt. The code is the same, why do I have such different results?

Sorry to bump, but I'm still a little lost with this - I expected it to be a bit more simple when I looked at the literature...