programming-for-dummies

Making User Interfaces with Event-Driven Programming 39
Unfortunately, although pull-down menus made programs easy for users,
they made writing programs much harder for the programmers:
Book I
Chapter 2
✦ Programmers had to write extra commands just to display all these
fancy pull-down menus and windows. (Even worse, programmers had to
make sure all those extra commands used to create pull-down menus
and windows actually worked correctly.)
✦ Programmers now had to write programs that could react to whatever
command the user chose. Rather than present the user with options in a
specific, predictable order, programs had to handle the unpredictable
choices of the user.
Different Methods
for Writing
Programs
To solve this dual problem of creating pull-down menus and knowing how to
handle the different commands the user might choose at any given time,
computer scientists developed event-driven programming.
In event-driven programming, an event is something that the user does, like
clicking a pull-down menu or clicking a button displayed in a window. Eventdriven
programming simply focuses on displaying different commands onscreen
and then handling these different events when they occur.
Event-driven programming divides programming into three distinct parts:
✦ The user interface: The commands the user sees on-screen
✦ The event handler: The part of your program that reacts to the commands
the user chooses from the user interface
✦ The actual program: The part of your program that actually does something
useful, such as drawing pictures or predicting the winners of horse
races
In the old days, creating a user interface essentially tripled your work:
1. Write your program.
2. Write commands to create a user interface.
3. Write commands to make your user interface actually work.
Event-driven programming eliminates this problem. Instead of forcing you to
write commands to display pull-down menus and windows on-screen, eventdriven
programming lets you visually design your user interface, such as the
number, placement, and size of buttons.