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Programming Microsoft® Visual Basic® 6.0 by Francesco Balena

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Callback and Subclassing

As you probably remember from the A World of Messages section near the beginning of this appendix, Windows deals with two types of messages: control messages and notification messages. Although sending a control message is just a matter of using the SendMessage API function, you'll see that intercepting a notification message is much more difficult and requires that you adopt an advanced programming technique known as window subclassing. But to understand how this technique works, you need to know what the AddressOf keyword does and how you can use it to set up a call-back procedure.

Callback Techniques

Callback and subclassing capabilities are relatively new to Visual Basic in that they weren't possible until version 5. ...

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