RAD Studio |  |

Declaring a Message Identifier

A message identifier is an integer-sized constant. Windows reserves the messages below 1,024 for its own use, so when you declare your own messages you should start above that level.

The constant WM_APP represents the starting number for user-defined messages. When defining message identifiers, you should base them on WM_APP.

Be aware that some standard Windows controls use messages in the user-defined range. These include list boxes, combo boxes, edit boxes, and command buttons. If you derive a component from one of these and want to define a new message for it, be sure to check the Messages unit to see which messages Windows already defines for that control.

Copyright(C) 2009 Embarcadero Technologies, Inc. All Rights Reserved.
What do you think about this topic? Send feedback!