_HORIZONTALLY SCROLLABLE LISTBOXES_
by Ted Faison


[LISTING ONE]

#ifndef __HLBOX_HPP
#define __HLBOX_HPP

#include <arrays.h>
#include <owl.h>
#include <listbox.h>

class THorizontalListBox: public TListBox {

  class Extent {
    int value;
  public:
    Extent(int i) {value = i;}
    Extent() {value = 0;}
    Extent(Extent& i) {value = (int) i;}
    int operator==(Extent& i) const {return value == (int) i;}
    int operator<(Extent& i) const {return value < (int) i;}
    operator int() {return value;}
    virtual int isSortable() {return 1;}
  };
  typedef BI_SArrayAsVector<Extent> Extents;
  Extents textExtents;
  int TextExtent(LPSTR);
  void UpdateHorizontalExtent();
public:
  THorizontalListBox(PTWindowsObject, int, PTModule = NULL);

  int AddString(LPSTR);
  int InsertString(LPSTR, int);
  int DeleteString(int);
  void ClearList();
  void InsertExtent(LPSTR);
  virtual WORD Transfer(void*, WORD);
};
#endif




[LISTING TWO]

#include "hlbox.hpp"

THorizontalListBox::THorizontalListBox(TWindowsObject* AParent,
  int id, TModule* module):TListBox(AParent, id, module),textExtents(20, 0, 20)
{
}
static void AddTextExtent(Object& AString, void* P)
{
  THorizontalListBox* listBox = (THorizontalListBox*) P;
  LPSTR string = (char*)(const char*)(RString)AString;
  if (AString != NOOBJECT)
    listBox->InsertExtent(string);
}
WORD THorizontalListBox::Transfer(void* DataPtr, WORD TransferFlag)
{
  WORD value = TListBox::Transfer(DataPtr, TransferFlag);
  if (TransferFlag == TF_SETDATA) {
    // for each string in the transfer buffer,
    // add its extent to the extent container
    TListBoxData* ListBoxData = *(PTListBoxData*) DataPtr;
    ListBoxData->Strings->forEach(AddTextExtent, this);
  }
  return value;
}
int THorizontalListBox::AddString(LPSTR AString)
{
  InsertExtent(AString);
  return TListBox::AddString(AString);
}
int THorizontalListBox::InsertString(LPSTR AString, int Index)
{
  InsertExtent(AString);
  return TListBox::InsertString(AString, Index);
}
void THorizontalListBox::InsertExtent(LPSTR AString)
{
  // store the extent of each string in sorted order in a container 
  int length = TextExtent(AString);
  Extent extent = *new Extent(length);
  textExtents.add(extent);
  // update the ListBox horizontal extent
  UpdateHorizontalExtent();
}
int THorizontalListBox::DeleteString(int Index)
{
  // find the text extent of the string to be deleted
  char string [256];
  GetString(string, Index);
  // remove the extent from the container
  Extent extent = Extent(TextExtent(string) );
  for (int i = 0; i < textExtents.getItemsInContainer(); i++) {
    if (extent == textExtents [i]) {
      textExtents.detach(extent, TShouldDelete::Delete);
      break;
    }
  }
  // update the ListBox horizontal extent
  UpdateHorizontalExtent();
  return TListBox::DeleteString(Index);
}
void THorizontalListBox::ClearList()
{
  // delete all the text extents in the container
  textExtents.flush();
  // update the ListBox horizontal extent
  UpdateHorizontalExtent();
  // Call DeleteString, to force Windows 3.0 to remove
  // the horizontal scrollbar. Windows 3.1 doesn't need this call
  DeleteString(0);
  // clear out the remaining strings in the ListBox
  TListBox::ClearList();
}
// find the extent of a ListBox string
int THorizontalListBox::TextExtent(LPSTR AString)
{
  int extent;
  // select the ListBox into the device context
  HDC hdc = GetDC(HWindow);
  HFONT hfont = (HFONT) SendMessage(HWindow, WM_GETFONT, 0, 0);
  if (hfont) {
    // non-system font being used: select it into the
    // ListBox's device context before calling GetTextExtent
    HGDIOBJ oldObject = SelectObject(hdc, hfont);
    // find the text extent of the string
    extent = GetTextExtent(hdc, AString, _fstrlen(AString) );
    // release resources used 
    SelectObject(hdc, oldObject);
    ReleaseDC(HWindow, hdc);
  }
  else {
    // system font in use: no font selection necessary,
    // because GetTextExtent will use the system font by default
    extent = GetTextExtent(hdc, AString, _fstrlen(AString) );
    ReleaseDC(HWindow, hdc);
  }
  return extent;
}
void THorizontalListBox::UpdateHorizontalExtent()
{
  int greatestExtent;

  // find the extent of the longest string in the
  // ListBox, and set the horizontal extent accordingly
  int lastElement = textExtents.getItemsInContainer() - 1;
  if (lastElement < 0)
    // no more strings in the ListBox
    greatestExtent = 0;
  else
    greatestExtent = textExtents [lastElement];
  // add a small amount of space, so that when ListBox is completely scrolled 
  // to the right, the last character is completely visible
  HDC hdc = GetDC(HWindow);
  greatestExtent += GetTextExtent(hdc, "X", 1);
  ReleaseDC(HWindow, hdc);
  // if the longest string fits completely in the ListBox, then scroll the box
  // completely to the left, so Windows will hide the scrollbar
  RECT rect;
  GetClientRect(HWindow, (LPRECT) &rect);
  int listWidth = rect.right - rect.left;
  if (listWidth >= greatestExtent)
    SendMessage(HWindow, WM_HSCROLL, SB_TOP, 0);
  // set the extent
  SendMessage(HWindow, LB_SETHORIZONTALEXTENT, greatestExtent, 0);
}




Figure 1: Required member functions for objects inserted into a sorted 
container 


Default constructor
Copy constructor
Operator ==
Operator <
isSortable()




Figure 2: Adding an extetent to the Extent container

int length = TextExtent(AString);
Extent extent = *new Extent(length);
textExtents.add(extent);
Figure 2: Adding an extetent to the Extent container

  int length = TextExtent(AString);
  Extent extent = *new Extent(length);
  textExtents.add(extent);