Chapter 15

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Chapter 15:
GUI Applications & Event-Driven Programming
Starting Out with Programming Logic & Design
Second Edition
by Tony Gaddis
Copyright © 2010 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
Chapter Topics
15.1 Graphical User Interfaces
15.2 Designing the User Interface for a GUI
Program
15.3 Writing Event Handlers
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15.1 Graphical User Interfaces
A Graphical User Interface (GUI) allows the user to
interact with the operating system and other programs
using graphical elements such as icons, buttons, and
dialog boxes
– Much of the work of a GUI is done through dialog boxes,
which are small windows that display information and
allow the user to perform actions
– In a command line interface, the programs determine the
order in which things happen
– In a GUI, the user can determine the order – this is called
event driven
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15.1 Graphical User Interfaces
Figure 15-3 A GUI program
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15.1 Graphical User Interfaces
Creating a GUI Program
– Most of the steps are the same
– But, the programmer also designs the GUI
elements that make up each window
– This includes the flow from window to window
Figure 15-4 A
user interface flow
diagram
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15.2 Designing the User Interface for a GUI
Interface
GUI development also includes the program’s
windows and all the graphical components
– In the past, this was a cumbersome process
– Newer languages allow for easier development
• Using Microsoft Visual Studio
– Visual Basic
– C++
– C#
• Using NetBeans and JBuilder
– Java
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15.2 Designing the User Interface for a GUI
Interface
Most IDE’s have a toolbox for easy development
Figure 15-5
Visually
constructing a
window in Visual
Basic
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15.2 Designing the User Interface for a GUI
Interface
Components are items that appear in a program’s
graphical user interface
–
–
–
–
–
–
Button: causes an action to occur when clicked
Label: can display text
Text Box: Allows the user to enter a single line of input
Check Box: Allows one or more options to be selected
Radio Button: Allows only one option to be selected
Combo Box: A dropdown list of items that the user can
select an item from, or enter input
– List Box: A list from which the user can select an item
– Slider: Allows the user to select a value from a range
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15.2 Designing the User Interface for a GUI
Interface
Figure 15-7 Various components in a GUI window
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15.2 Designing the User Interface for a GUI
Interface
Component names are used to identify the
components in the program, in the same way
variable names are used
Figure 15-8
Components
and their
names
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15.2 Designing the User Interface for a GUI
Interface
Properties can be set on components to modify
how it appears on the screen
– Sets things like color, size, and position
A summary of constructing a window
– Sketch the window
– Create the necessary components and name them
– Set the components’ properties to the desired
values
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15.3 Writing Event Handlers
Event handlers are written to control the GUI
– After the windows are designed, event handlers are
coded to respond to events when an action occurs,
such as clicking a button
– Event: an action that takes place within a program
– Event handlers: a module that automatically
executes when a specific event occurs
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15.3 Writing Event Handlers
How to write the event handler module
Module ComponentName_EventName()
The statements that appear here
are executed when the event occurs.
End Module
//an event handler that closes a window
Module exitButton_Click()
Close
End Module
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