Borland® Delphi™ 6 Developer's Guide

Handling Messages

Handling or processing a message means that your application responds in some manner to a Windows message. In a standard Windows application, message handling is performed in each window procedure. By internalizing the window procedure, however, Delphi makes it much easier to handle individual messages; instead of having one procedure that handles all messages, each message has its own procedure. Three requirements must be met for a procedure to be a message-handling procedure:

• The procedure must be a method of an object.
• The procedure must take one var parameter of a TMessage or other message-specific record type.
• The procedure must use the message directive followed by the constant value of the message you want to process. ...