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Visual Basic's Windows format, with its point and click graphics interface, gives DOS-based programs a new look. You can design structures by applying drawing elements, like lines or rectangles, without having to write a list of special instructions for the computer to generate them from scratch, as in BASIC, for example.
Visual Basic also includes the engine from the database system development kit known as Access, from Microsoft. Access gives you a direct line to many database formats. And Visual Basic supports new custom controls, including ActiveX Controls. Plus it lets you access the functions and structures of the Windows Applications Programming Interface (API).
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Typically, the user selects from available options by clicking on active objects -- such as menus, command buttons, scroll bars, text boxes, dialog boxes, icons, or the form itself -- to trigger events to which the program responds. The mouse events activate program lists, or scripts, that have been prepared to produce anticipated responses. User action (or possibly also a system event) can interrupt routine programming, so the flow is dictated more directly by the user. Although code still has to be written for the events -- you need a car if you wish to drive one -- the automation creates more of an atmosphere of free choice.
An event is an action "recognized" by the object. In Visual Basic, each object has associated with it a predefined set of mouse events, like single or double clicks, mousedowns, mouseups, and the like. If one of these events occurs, the event-driven program executes code in response to it. The units of code that are executed are said to be procedures.
An event signals that an action is to be taken on an object, and the action depends on the code written for it. As a program designer, you define the response by the way you spell out the code. So if no code is written for the mouse event, no action can be taken on it.
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Visual Basic is an object oriented system that lets you focus on the graphics you might wish to produce rather than on the programming used to produce it. It has a highly developed graphical user interface (GUI) with a flexible, and direct representation of tools to take use the Windows graphical environment.
Defined as a combination of code and data that can be treated as a unit, an object involves things like command buttons, forms, databases, charts, or the like. Each object is a member of a class -- like the class of command buttons. The class identifies a set of characteristics and capabilities shared by its members, namely properties, methods, and events.
The sense of a class is just as we normally understand it in ordinary affairs, like the class of all men, or the graduating class of '96. The members are instances of the class and exhibit the class nature, yet each has its own specifications. Some students, for example, are taller or heavier than others, but they are still students.
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In Visual Basic, a viewable unit has a number of special properties, like the following:
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Controls, Indicators, Supports
Controls
are things like command buttons, option buttons, list boxes, pull-down menus, dialog boxes, text boxes, labels, picture boxes, check boxes, timer, lines, or shapes, on which action can be taken by the user, say by clicking on them with the mouse. They are the things directly affected by the user. For example, a command button may be clicked to start the trajectory of a tennis ball.Indicator objects
are picture items not directly affected by the user, but which can change as a consequence of the user's action. They are items that represent things like a tennis ball, tennis racket, thermometer, pressure gauge, altimeter, moving parts of a machine, missile, odometer, radiation counter, fire hose, hand, arm, body, or robot -- objects that can be made to react in response to action taken in the real environment. The visual effects would indicate relevant changes in the environment of the objects, like the motion of the ball across the screen.Also part of the display are obvious things that I call supporting structures -- the "other" elements that represent things in the environment needed to perform skills but are neither active (as controls) nor change as a result of actions (like the indicators). They would include entities like a tennis court surface and net, a football stadium, an airport landing strip, a house or its furniture, the concert hall stage and seats, or the like, that support skills involving them.
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You can work directly with display objects and manipulate them in a variety of ways. Each object is a member of an object class, and each type has its list of properties, in terms of which you can construct the instances. For example, you can select specific text, like a single letter, and assign to it a particular font size or color. You can also choose to underline or italicize it, or make it regular or bold. You can do the same thing with paragraphs, or an entire document -- the kinds of things you can do using word processors and drawing programs.
Lines, too, can have several different property values -- like style, color, and thickness. You can select straight or curved lines. Circles can be filled in or left open. Most objects can be enabled or dis-enabled. They can be rendered visible or invisible, or placed in the foreground or in the background. And of course they can be sized, or colored. You can also turn objects into "hotspots," which are index devices that can be clicked to reach related information.
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Visual Basic has a modular construction and is event driven. It consists of structural devices called modules and procedures, as summarized as in the following.
Structural Characteristic of Visual Basic for Windows.
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