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Chapter 28. Responding to Events with VB... > In the Real World—Dealing with Event...

In the Real World—Dealing with Event-Driven Programming

Beginning programmers and Web page designers often find that understanding Windows' event-driven programming model to be quite difficult. The same problem befalls many programmers experienced in conventional procedural languages, such as assembly, COBOL, Pascal, and xBase. With a very few exceptions, VBA code in an Access application or script in a DHTML page executes only in response to a predefined event. (The primary exceptions are variable and Windows function prototype declarations that precede VBA subprocedure and function code in modules.)

Early versions of Access and Visual Basic offered a relatively sparse event model, and DAO doesn't fire events in any version. Each upgrade to Access and Visual Basic added to the platform's events, a process described in press releases as "increasing event granularity." The OLE Controls of Access 2.0 and Visual Basic 4.0 were in-process Automation servers with event sources. Forms and other containers for OLE Controls came to be known as event sinks. The source-sink nomenclature derives from the early days of transistors—emitters serve as a source of electrons and collectors act as electron sinks. Field effect transistors gained electron drains, and other devices had electron traps. Familiarity with plumbing fixtures, along with solid-state physics and thermodynamics, was de rigeur to a basic understanding of semiconductor theory.


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