4003-707-02 Advanced Programming
Module 5. GUIs -- Lecture Notes

The MVC Pattern

• Model: the core classes

• View: the GUI classes

• Controller: the stuff that hooks the core and the GUI together

• Controller composed of listeners
  • GUI listeners -- change core state in response to user input
  • Core listeners -- update GUI when core state changes

• The processing loop for user actions
  • User does an input action (mouse click, key press, . . .)
  • AWT thread calls a method on a GUI listener in the controller
  • GUI listener calls a method on a core object
  • Core object changes core state
  • Core object calls a method on a core listener in the controller
  • Core listener calls a method on the GUI object
  • GUI object updates GUI (repaint display, enable button, . . .)

• Core initiated actions
  • Timer thread calls a method on a core object
  • Core object changes core state
  • Core object calls a method on a core listener in the controller
  • Core listener calls a method on the GUI object
  • GUI object updates GUI (repaint display, enable button, . . .)

Java Swing

• The window: Class javax.swing.JFrame

• Widgets within the window held in a container
  • For example, class javax.swing.JPanel

• A container has a layout manager
  • Determines where the widgets will be displayed within the container
  • For example, class javax.swing.BoxLayout
  • Many other layout managers available

• Useful JPanel attributes
  • Border
  • Background color

• Adding widgets to a JPanel with a BoxLayout
  • BoxLayout.X_AXIS: Widgets appear from left to right
  • BoxLayout.Y_AXIS: Widgets appear from top to bottom
  • A JPanel may contain other JPanels, to organize widgets hierarchically
  • Adding gaps between widgets

• Examples of Java Swing widgets
  • Class javax.swing.JButton -- button
  • Class javax.swing.JTextField -- edit box
  • Class javax.swing.JSpinner -- edit box with up and down buttons
  • Class javax.swing.JComboBox -- box with drop-down menu
  • Class javax.swing.JLabel -- fixed label
  • Class javax.swing.JMenu, javax.swing.JMenuBar -- menus
  • Many others

• JFrame pack() method

• JFrame setVisible() method

Handling User Input with Java Swing

• Java Swing itself uses the MVC pattern
  • Add listeners to widgets

• Respond to an action on a widget
  • For example, a button was pressed
  • addActionListener() method
  • Interface java.awt.event.ActionListener
  • Class java.awt.event.ActionEvent

• Respond to a change within a widget
  • For example, a spinner's value went up or down
  • addChangeListener() method
  • Interface javax.swing.event.ChangeListener
  • Class javax.swing.event.ChangeEvent

• Respond to a mouse click (in a widget that doesn't do anything else with mouse clicks)
  • For example, mouse was clicked in a graphical output panel
  • addMouseListener() method
  • Interface java.awt.event.MouseListener
  • Class java.awt.event.MouseAdapter
  • Class java.awt.event.MouseEvent

• Respond to a keystroke (rather than let the widgets themselves handle it)
  • The keyboard focus
  • Class java.awt.KeyboardFocusManager
  • Class java.awt.KeyEventDispatcher
  • Class java.awt.event.KeyEvent

• Respond to actions on the window (JFrame)
  • Interface java.awt.event.WindowListener
  • Class java.awt.event.WindowAdapter
  • Class java.awt.event.WindowEvent

• Widget listeners delegating to GUI listeners

• The processing loop for user actions, more detail
  • User does an input action (mouse click, key press, . . .)
  • AWT thread calls a method on the widget's listener
  • Widget listener calls a private method in the GUI object
  • Private method calls a method on a GUI listener in the controller
  • GUI listener calls a method on a core object
  • Core object changes core state
  • Core object calls a method on a core listener in the controller
  • Core listener calls a method on the GUI object
  • GUI method calls repaint() on the display
  • Core listener calls another method on the GUI object, maybe
  • GUI method calls setEnabled() on a button

• At a later time, not part of the above chain of calls:
  • AWT thread notices a widget needs repainting
  • AWT thread calls widget's paintComponent() method
  • For class edu.rit.swing.DisplayablePanel, paintComponent() method calls Displayable object's draw() method
  • draw() method draws stuff in DisplayablePanel's graphics context

Advanced Programming • 4003-707-02 • Fall Quarter 2008

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Alan Kaminsky • Department of Computer Science • Rochester Institute of Technology • 4486 + 2220 = 6706

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Copyright © 2008 Alan Kaminsky. All rights reserved. Last updated 07-Oct-2008. Please send comments to ark­@­cs.rit.edu.