PageCounter Object for ScrollViews

This article was contributed by [Volker Voecking].

When scrolling in a document that consists of quite a lot pages it might be helpful for the user to get an information which page of the document would be displayed if he/she would release to slider of the scrollbar at a certain position.
Microsoft Word has such a feature. It's a tooltip-like window that displays the page number that corresponds to the current position of the slider during scrolling.

I implemented a class named CScrollViewPageCounter that displays such a page number in a window that looks like a tooltip-window. If you have a look at the source code you'll find out that it was quite easy to implement. The code itself is self-explanatory...

HOW TO USE

To use the ScrollViewPageCounter-Object you have to perform the following steps:

1. Add the files ScrollViewPageCounter.h and ScrollViewPageCounter.cpp to your project.

2. Add a new member m_pScrollViewPageCounter to your scroll view class.

   CScrollViewPageCounter* m_pScrollViewPageCounter;

Of course your have to include the corresponding header file here as well:

   #include "ScrollViewPageCounter.h"

3. Create the page counter object in CYourScrollView::OnInitialUpdate()

   BOOL CYourScrollView::PreCreateWindow(CREATESTRUCT& cs)
   {
      CScrollView::OnInitialUpdate();

      // Instantiate the counter object
      m_pScrollViewPageCounter = new CScrollViewPageCounter( this );
    }

4. Add a command handler for the message WM_VSCROLL:

   void CYourScrollView::OnVScroll(UINT nSBCode, UINT nPos, CScrollBar* pScrollBar) 
   {
      if ( nSBCode == SB_THUMBTRACK )
      {
         // calculate page number (insert your algorithm here)
         UINT uiPageNumber = (UINT) (nPos / 10) + 1;

         // display page number 
         m_pScrollViewPageCounter->DisplayPageNumber( uiPageNumber );
      }

      // when scrolling is finished we have to hide the page counter
      if ( nSBCode == SB_ENDSCROLL )
         m_pScrollViewPageCounter->Reset();
	
      CScrollView::OnVScroll(nSBCode, nPos, pScrollBar);
   }