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Q81707: INFO: WM_CTLCOLOR Processing for Combo Boxes of all Styles

Article: Q81707
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.0,3.1
Operating System(s): 
Keyword(s): kb16bitonly kbComboBox kbCtrl kbSDKPlatform kbGrpDSUser
Last Modified: 06-NOV-1999

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The information in this article applies to:

- Microsoft Windows Software Development Kit (SDK) versions 3.1, 3.0 
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SUMMARY
=======

Windows sends a WM_CTLCOLOR message to the parent of a control window to enable
the parent to specify the color of the control. A notification code, which is
the value of the high-order word of the lParam, accompanies the WM_CTLCOLOR
message to indicate the control type for a WM_CTLCOLOR message. Windows does not
define a notification code that enables an application to change the color of a
combo box control. However, Windows sends WM_CTLCOLOR messages to a combo box
control that relate to its component parts: one message for the list box portion
and, if applicable, another message for the edit control portion. An application
can subclass the control to intercept and process these messages. This article
discusses how to perform the subclassing and how to address the problems that
arise when an application changes the colors of a combo box under Windows 3.0.

MORE INFORMATION
================

Under Windows versions 3.0 and later, Windows sends a WM_CTLCOLOR message to a
combo box for each of its individual elements. An application can subclass the
combo box control to process the message. The text below discusses each of the
combo box styles and how the color can be changed for each style.

CBS_SIMPLE Style
----------------

Under Windows 3.0, an application must process three WM_CTLCOLOR notifications
codes, CTLCOLOR_EDIT, CTLCOLOR_MSGBOX, and CTLCOLOR_LISTBOX, to change the
colors for a CBS_SIMPLE-style list box. Under Windows 3.1, the application is
not required to process the CTLCOLOR_MSGBOX notification.

Each time the application processes a notification, it must set the foreground
and background colors, using SetTextColor and SetBkColor, respectively. The
wParam accompanying the WM_CTLCOLOR message contains a handle to the appropriate
display context. In addition, the application must return a valid handle to the
appropriate background brush that Windows will use to paint those areas not
occupied by text.

CBS_DROPDOWN Style
------------------

To change the colors of a CBS_DROPDOWN-style combo box under Windows 3.0, process
the same three notifications as for the CBS_SIMPLE combo box. However, there is
a difficulty with regard to setting the text color. In the drop-down list box,
the colors set with SetBkColor and SetTextColor are not used. Instead, the combo
box uses the system default colors. As a workaround, change the combo box to the
owner-draw style. Process the WM_DRAWITEM message to draw the individual items
with the desired text colors.

For more information on using an owner-draw combo box in an application, query on
the following words in the Microsoft Knowledge Base:

  prod(winsdk) and owncombo

Under Windows 3.1, it is not necessary to use an owner-draw combo box. The
application can process the CTLCOLOR_EDIT and CTLCOLOR_LISTBOX notifications to
change the color of a combo box.

CBS_DROPDOWNLIST Style
----------------------

To change the color of a CBS_DROPDOWNLIST-style combo box, process the
CTLCOLOR_LISTBOX notification. However, the application must process this
notification in the combo box subclass procedure and in the window procedure for
the parent window of the combo box.

Under Windows 3.0, the text color problem discussed above for CBS_DROPDOWN-style
combo boxes is evident for CBS_DROPDOWNLIST combo boxes. To address this
problem, the application must use an owner-draw combo box.

Although it is not necessary to use an owner-draw combo box under Windows 3.1,
the application must process the CTLCOLOR_LISTBOX notification in both the combo
box subclass procedure and in the window procedure for the parent window of the
combo box.

NOTE: WM_CTLCOLOR with codes is obsolete in Win32. Each code now has its own
message, such as WM_CTRLCOLORBTN, WM_CTLCOLORLISTBOX, and so forth. Otherwise,
things work the way they do in Windows 3.1.

Additional query words: combobox listbox

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Keywords          : kb16bitonly kbComboBox kbCtrl kbSDKPlatform kbGrpDSUser 
Technology        : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310
Version           : WINDOWS:3.0,3.1
Issue type        : kbinfo

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