Advantages of event-driven programs
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The three major kinds of user interfaces are
Command-line, where the user types commands at a prompt. The MS-DOS operating system, the dBASE Dot Prompt (in DOS versions) and Command window (in Windows versions), are examples of command-line interfaces.
Menu-driven, where the user selects choices from a hierarchy of menu items. Most applications written using prior versions of dBASE provide menu-driven interfaces.
Event-driven, where the user interacts with visible objects, such as forms containing pushbuttons and list boxes, in any sequence. The user interface is event-driven, and you can create event-driven applications using the dBASE language.
Using traditional programming techniques, you can build menu-driven user interfaces. In these applications, the program dictates the sequence of events. If the user selects Order Entry from a menu, the program typically walks through a series of screens asking the user for information: enter the customer name, enter the date and purchase order number, enter the line items, enter the shipping charge.
These menu-driven techniques are not well-suited for programming in event-driven environments such as Windows. In an event-driven application, the user controls program flow. A user can click a button, activate a window, or select a menu choice at any time, and the program must respond to these events in whatever sequence they occur.
In a well-designed event-driven application,
The user can focus on the task, not on the application. The user doesn’t have to learn a complex hierarchy of menu choices. Rather, when choosing to enter an order, the user sees an order form similar to a familiar paper form.
The user doesn’t need to re-learn how to perform tasks. Because you create an application’s interface using familiar objects such as pushbuttons and list boxes, common operations—opening a file, navigating a form, exiting the application—are more consistent across applications.
Most important, event-driven interfaces reflect the way people work in the real world. When clerks write up orders, they pick up forms and fill them out. When they receive checks for orders, they pick up the invoices and mark them as paid. This natural flow of work follows an object-action pattern. That is, a clerk selects an object (an order form, an invoice) and performs some action with it (fills out the order, posts the check).
Likewise, in an event-driven application, the user selects objects (forms, entry fields, pushbuttons) and performs actions with them.