Adding an MFC Message Handler
You can use the Class Wizard or the Properties window in CLass View to add a message handler (a member function that handles Windows messages) to a class and map Windows messages to the message handler. You can also add an event handler for any dialog box control.
By using the Class Wizard or Properties window (in Class View) to define message- and event-handling functions, you can automatically update the message-dispatch table (or message map) and your class header file.
Note
You can add a message handler to an ATL class using the Class Wizard; however, some results may vary. For more information, see the ATL topic Adding an ATL Message Handler.
Adding Functionality with Code Wizards
Adding a Class
Adding a Member Function
Adding a Member Variable
Overriding a Virtual Function
Navigating the Class Structure
Dialog Editor