SAMPLE: Right and Decimal-Alignment in Owner-Draw Controls

The information in this article applies to:

• Microsoft Windows Software Development Kit (SDK) for Windows versions 3.0 and 3.1

SUMMARY

In the Microsoft Windows graphical environment, the primary feature of an owner-draw control is the ability to customize the manner that a control displays information and to extend its capabilities. An example of a customized presentation is to decimal align a column of numbers in an owner- draw list box. This article describes how to perform this alignment, and then describes some example code in the Microsoft Software Library.

ODLIST2 is a file in the Microsoft Software Library that demonstrates this method to right align a substring of digits. The ODLIST2 application implements a horizontally scrollable list box that contains a small database of account records. The titles of the "Account", "Balance", and "Name" fields scroll with their associated column data because the application subclasses the main database list box to process WM_HSCROLL messages. When a scroll message is received by the data list box, it sends a corresponding WM_HSCROLL message to the title list box.

Download ODLIST2.EXE, a self-extracting file, from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download ODLIST2.EXE (size: 33504 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get ODLIST2.EXE (size: 33504 bytes) 
  

MORE INFORMATION

To right align a string (of digits or of text) at a particular horizontal position "X," the application must compute the length of the string. Then, move that distance to the left of "X" before drawing the string. The width of a string is contained in the low-order word of the value returned by the GetTextExtent() or GetTabbedTextExtent() functions.

For example, if the following are true

   X         is the horizontal position for the right edge of the
                text
   hDC       is a handle to a device context
   szDigits  is an array of characters

   X - LOWORD(GetTextExtent(hDC, szDigits, lstrlen(szDigits))

     123.45
    6543.12

   (the desired right position) - (the width of the substring)

The code sample below implements a tab stop before a digit substring. To use this code, place it into the code that processes the WM_DRAWITEM message for an owner-draw list box with the LBS_USETABSTOPS style:

   nWidth     is the width (x-extent) of the digit substring.
   lpdis      is the far pointer to a DRAWITEMSTRUCT obtained as the
                 lParam in a WM_DRAWITEM message.
   nTabStops  is an integer array of tab stops. If the current mapping
                 mode is MM_TEXT, the values in the array are in
                 pixels.

   // Get the x extent of digit substring
   nWidth = LOWORD(GetTextExtent(lpdis->hDC, szDigits,
                lstrlen(szDigits)));

   // Set first tab stop to align the right side of the digit
   // substring with the right border of the list box
   nTabStops[0] = X - nWidth;

   // Draw digit string at tabbed position
   TabbedTextOut(lpdis->hDC, lpdis->rcItem.left, lpdis->rcItem.top,
        (LPSTR)szDigits, lstrlen(szDigits), 1, (LPINT)nTabStops);