Substandard Techniques for Exposing Custom Controls

Description of substandard techniques for exposing custom controls.

If an application does not support Microsoft® Active Accessibility®, it may not be fully accessible. The following techniques render controls partially compatible:

• Return a descriptive string when the control is queried by using the WM_GETTEXT message. For example, allow a custom equivalent of a button control labeled "Print" to return the string "Print button." This identifies both control type and label. The same string is appropriate for a button with a label that is something other than text, such as a graphic of a printer. Similarly, allow a custom control that behaves like a check box to return the caption string "Printing Enabled check box, checked."

• Support the WM_GETDLGCODE message, identifying the keyboard input that is supported. For example, allow a custom equivalent of an edit control to handle WM_GETDLGCODE by returning DLGC_HASSETSEL if it handles messages to set the selection, DLGC_WANTARROWS if it uses arrow keys, and DLGC_WANTCHARS to indicate that it uses character input.

  Note: Only controls that have their own window handles can respond to the WM_GETTEXT and WM_GETDLGCODE messages.

To avoid compatibility problems with accessibility aids, you should follow Active Accessibility guidelines closely when designing custom controls. For more information about how to avoid compatibility problems with accessibility aids, see the Accessibility section of the MSDN® Library.