Scrollbars, using the WS_HSCROLL and WS_VSCROLL styles

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Overview

All CWnd derived classes have access to system supplied scrollbars by using the window styles WS_HSCROLL and WS_VSCROLL, but these are no ordinary scrollbars! For starters, you cannot get a CScrollBar* pointer to them, so they cannot be subclassed.

Included above is a project that makes use of these standard scrollBar objects got by using these window styles. Its a view which creates a window derived from CWnd which has the necessary functions to enable/disable the scrollbars as required. As you re-size the view, this re-sizes the window which decides whether the scrollbars should be shown.

Windows acts oddly when enabling/disabling the scrollbars. When you decide you need to show one or both of the scrollbars by using the CWnd::ShowScrollBar method, a WM_SIZE message is automatically generated and called immediately telling your window the new size of the client area (which does not include the area taken by the scrollbars if visible), so if you choose to show/hide the scrollbars in the OnSize handler, the function needs to avoid problems due to recursion.

User interface

Scrollbars are a standard part of the windows user interface. I was trying to use one of these in a control and needed the scrollbar thumb to show how much of the total area was displayed. The standard MSDN documentation on how to do this was sadly lacking (or I was just dumb). I spent many hours in frustration which ended in a rant in the Soapbox. From a sympathetic reply there, I was given the clue on how to do what I had been attempting.

Scrollbars can be setup using a SCROLLINFO object to set the range and thumb size. Its just that the flags you can set and the variables are very badly documented. So here is an overview of what I have learnt. The SCROLLINFO structure looks like this:

typedef struct tagSCROLLINFO { 
    UINT cbSize; 
    UINT fMask; 
    int  nMin; 
    int  nMax; 
    UINT nPage; 
    int  nPos; 
    int  nTrackPos; 
    }   SCROLLINFO, *LPSCROLLINFO; 

A point by point description of these are:

My problem was I was trying to get the thumb to be proportional, which is good programming procedure for all new windows applications. This allows more information to be supplied to the user in how much data is not being shown. As another CP user replied to me: I hate programmers who don't do this - they should be taken out and shot!, or words to that effect.

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