ODVHLB Demonstrates Owner-Draw Variable-Height List Box

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

ODVHLB is a file in the Microsoft Software Library that demonstrates using an owner-draw variable-height list box in an application for the Microsoft Windows environment.

In the ODVHLB application, the user can add a short string (one line of text), long string (two lines of text), or an icon to a list box. Because the list box has the LBS_MULTIPLESEL style, the user can select multiple items in the list box simultaneously.

Download ODVHLB.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 ODVHLB.EXE (size: 26949 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get ODVHLB.EXE (size: 26949 bytes) 
  

MORE INFORMATION

To implement an owner-draw variable-height list box, an application must process the WM_MEASUREITEM and WM_DRAWITEM messages in the window procedure for the list box's parent window. When the list box has the LBS_OWNERDRAWVARIABLE style, the parent window receives a WM_MEASUREITEM and a WM_DRAWITEM message each time the application updates an item in the list box.

When the parent of the list box receives a WM_MEASUREITEM message, lParam points to a MEASUREITEMSTRUCT data structure. The application must specify values for the itemHeight and itemWidth members of this structure to indicate how much space in the list box Windows must allocate for the item. Through the WM_MEASUREITEM message, the application can individually specify the height of each item in the list box.

The parent of the list box receives a WM_DRAWITEM message when an item in the list box needs to be drawn. The lParam parameter points to a DRAWITEMSTRUCT data structure. The itemAction member indicates the required drawing action and itemState member indicates the visual state of the item. For example, when the itemAction member is ODA_SELECT and the itemState member has the ODS_SELECTED flag set, the selection state has changed and the item is gaining selection. Conversely, if the itemState member has the ODS_SELECTED flag clear, the item is losing selection.

The itemData member of the DRAWITEMSTRUCT data structure identifies the item in the list box, either through a pointer to a string or a 32-bit identifier. An application specifies an appropriate identifier when it uses the LB_ADDSTRING or LB_INSERTSTRING message to add an item to the list box.