CDoubleScrollBar: Scrollbars based on double values

• Download demo project - 15 Kb
• Download source - 2.76 Kb

Introduction

After recently adding scrollbars to my final year project, I realized that I needed to use a scrollbar which can recognize double values instead of ints. I checked through the MSDN archive, and could find no direct way of supporting this. So I decided to write my own class, derived from CScrollBar.

The code

Reading the MSDN, it informs me that the maximum range of int values is 32767 (which I find highly skeptical, as their holding values are 32 bit), and so I have merely subdivided the range in double, by the maximum number of int values. This variable is editable, nPrecision defined in the constructor.

The following methods are overridden, compared here with there original int form...

double CDoubleScrollBar::GetScrollLimit();
    // Compared with ...

int CScrollBar::GetScrollLimit();

double  CDoubleScrollBar::GetScrollPos() const;
    // Compared with ...

int CScrollBar::GetScrollPos() const;

void CDoubleScrollBar::GetScrollRange(double * dMinPos, double * dMaxPos);
    // Compared with ...

void CScrollBar::GetScrollRange(LPINT lpMinPos,LPINT lpMaxPos) const;

double CDoubleScrollBar::SetScrollPos(double dPos, bool bRedraw = true);
    // Compared with ...

int CScrollBar::SetScrollPos(int nPos,BOOL bRedraw = TRUE);

void CDoubleScrollBar::SetScrollRange(double dMinPos, 
                        double dMaxPos, bool bRedraw = true);
    // Compared with ...

void CScrollBar::SetScrollRange(int nMinPos,
                 int nMaxPos,BOOL bRedraw = TRUE);

Note: Please do not attempt to use GetScrollInfo() and SetScrollInfo() to obtain information about the scrollbar, if you wish to obtain their double values. These methods have not been overridden, and return the original values in int.

To provide the functionality that has been lost with Get/SetScrollInfo(), I have written three methods, which also make changing the scrollbar easier.

double  CDoubleScrollBar::GetPageSize();
void CDoubleScrollBar::SetPageSize(double dPageSize,bool bRedraw);
double CDoubleScrollBar::GetTrackPos();

double CDoubleScrollBar::GetPageSize();. This returns the size of the page (the block that you drag) in double value. This replaces the segment of code...

SCROLLINFO siTemp;
m_ScrollBar.GetScrollInfo(&siTemp,SIF_PAGE);
int nPageSize = siTemp.nPage;

void CDoubleScrollBar::SetPageSize(double dPageSize,bool bRedraw);. This sets the size of the page, and causes the scrollbar to be redrawn if bRedraw is true. This replaces the segment of code...

SCROLLINFO siTemp;
siTemp.nPage = nPageSize;
siTemp.fMask = SIF_PAGE;
m_ScrollBar.SetScrollInfo(&siTemp, bRedraw);

double CDoubleScrollBar::GetTrackPos();. This returns the position of the scrollbar when the user is tracking (SB_THUMBTRACK). Using this method when the user is not tracking causes unpredictable output. It replaces the segment of code (found in OnHScroll()/OnVScroll()) ...

SCOLLINFO siTemp;
m_ScrollBar.GetScrollInfo(&siTemp,SIF_TRACKPOS);
int nCurrentTrackPos = siTemp.nTrackPos;

Implementing this code in your project is quite simple. Just add the .cpp and .h files to your project, #include "DoubleScrollBar.h" in your .h files which will use the DoubleScrollBars, and create away.

Limitations

The main limitation is that you cannot (as yet) create member values of CDoubleScrollBar as doubles and you have to use the extra functions to overcome the lack of a DOUBLESCROLLINFO structure.

Please comment and send bug reports / fixes here &| at dbh@cs.stir.ac.uk.

Enjoy.