Concepts of Programming Languages
Lecture 20 - Event-Driven Programming
Patrick Donnelly
Montana State University
Spring 2014
Patrick Donnelly (Montana State University) Concepts of Programming Languages Spring 2014 1 / 37
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Event-Driven Programming: An Introduction to Handling Events in Java and C#, Exercises of Programming Languages
A lecture note from Montana State University's Spring 2014 'Concepts of Programming Languages' course, focusing on event-driven programming. The note covers the concept of event-driven programming, event handling, event sources, event properties, and provides examples using Java Swing and C#. Students will learn about event sources, event properties, and how to handle events using Java Swing and C#.
What you will learn
- What are event sources in programming?
- What are the properties of event-driven programs?
- How do you handle events in C#?
- What is event-driven programming?
- How does event handling work in Java?
Typology: Exercises
2021/2022
1 / 37
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Concepts of Programming Languages
Lecture 20 - Event-Driven Programming
Patrick Donnelly
Montana State University
Spring 2014
Administrivia
Assignments:
Programming #4 : due 04.
Reading:
Chapter 14
Event-Driven Programming
A conventional model of computation has the program prescribe the exact order of input.
Programs terminate once the input is exhausted.
Event-driven programs do not control the sequence in which input events occur.
Event Handling
Definition
An event is a notification that something specific has occurred, such as a mouse click on a graphical button.
Definition
The event handler is a segment of code that is executed in response to an event.
Imperative and Event-Driven Paradigms Contrasted
Event Sources
Input to an event-driven program comes from autonomous event sources.
Events occur asynchronously.
Example: human, robot sensors, engine sensors
Model-View-Controller (MVC)
Model: the object being implemented. Ex: game, calculator.
Controller: input mechanisms. Ex: buttons, menus, combo boxes.
View: output.
Ex: Tic-Tac-Toe Model
Whose turn is it?
State of the board.
Has someone won?
Are there no empty squares?
Java Swing GUI Components
Text box is an object of class JTextField
Radio button is an object of class JRadioButton
Applet’s display is a frame, a multilayered structure
Content pane is one layer, where applets put output
GUI components can be placed in a frame
Layout manager objects are used to control the placement of components
The Java Event Model
Definition
User interactions with GUI components create events that can be caught by event handlers, called event listeners.
An event generator tells a listener of an event by sending a message
An interface is used to make event-handling methods conform to a standard protocol
A class that implements a listener must implement an interface for the listener
Java Class AWTEvent and Its Subclasses
The Java Event Model
One class of events is ItemEvent, which is associated with the event of clicking a checkbox, a radio button, or a list item
The ItemListener interface prescribes a method, itemStateChanged, which is a handler for ItemEvent events
The listener is created with addItemListener
Components and their Event Handlers
Widget Listener Interface JButton ActionListener actionPerformed(ActionEvent e)
JComboBox ActionListener actionPerformed(ActionEvent e)
JLabel MouseListener mouseClicked(MouseEvent e) mouseEntered(MouseEvent e) mouseExited(MouseEvent e) mousePressed(MouseEvent e) mouseReleased(MouseEvent e) MouseMotionListener mouseDragged(MouseEvent e) mouseMoved(MouseEvent e)
JTextArea ActionListener actionPerformed(ActionEvent e)
JTextField ActionListener actionPerformed(ActionEvent e)