scott grissom, copyright 2004ch 12: swing slide 1 how do i learn gui development? use these lecture...

Scott Grissom, copyright 2004 Ch 12: Swing Slide 1

How do I learn GUI development?

• Use these lecture notes to supplement chapter 12

• Refer to the online documentation available from the course web site

• Use the sample code available on the EOS machines

~grissom/163/Demos


Java JFC/Swing

• Java provides strong support for building GUIs through the javax.swing package

• Platform independencesame code

same appearance

• The book covers:containers (12.2.2)

layout managers (12.2.3)

event classes (12.4)

listener classes (12.4)

GUI components (12.3)


Event-Driven Programming

• Events signal important user actions, like a mouse click

• Listeners contain methods that respond to specific events

• GUI components are the screen elements that a user manipulates with the mouse and keyboard

• Layout managers govern how the components appear on the screen


Containers (12.2.2)

• A container is a special category of GUI components that hold other components

• A Japplet is a container used for applets

• A JFrame is used for an application

• A JPanel is used to group related components together for appearances


Layout Managers (12.2.3)

• One approach is to explicitly place componentssetLocation(int x, int y)

wrt to upper left corner

this is discouraged!

• Java JFC layout is dynamic to allow for different screen sizes and platformsautomatically sizes and places components

• There are several layout managers to choose from:flow layout

border layout

grid layout

box layout (not in book)

• Each container has a particular layout manager as default


Flow Layout

• Components are placed in a row from left to right in the order in which they are added

• New rows are created as needed

• Flow layout is the default layout for JPanels and Japplets

• Components are displayed at their preferred size

• Refer to sample code ~grissom/163/Demos/flowLayout.java


Border Layout

• Defines five locations where a component can be addedNorth, South, East, West, and Center

• The programmer specifies the area in which a component should appearadd(BorderLayout.NORTH, comp)

• Only one component per location

• Components expand to full size

• Use a JPanel to hold more than one

• Default for JFrame

• Refer to sample code ~grissom/163/Demos/borderLayout.java


JPanels

• Place multiple components inside a Panel

• Set the layout manager

• Sample CodeJPanel p = new JPanel();

p.setLayout(new FlowLayout());

Jbutton b1 = new Jbutton(“one”);

Jbutton b2 = new Jbutton(“two”);

p.add (b1);

p.add (b2);

getContentPane().add(p,BorderLayout.NORTH);

• Refer to sample code ~grissom/163/Demos/panelLayout.java


Box Layout

• Not covered in book

• Components are placed in a row OR a column as specified

• Create space between componentsBox.createRigidArea()

Box.createHorizontalGlue()

• Sample CodeBoxLayout b;

b = new BoxLayout(this, BoxLayout.X_AXIS)

• Refer to sample code ~grissom/163/Demos/boxLayout.java


Grid Layout

• Components are placed in a grid with a user-specified number of columns and rows

• Each cell is the same size

• Components placed left to right and top to bottom

• GridBag layout is a more advanced managerFeel free to experiment


The Big GUI Picture

• Refer to the sample code on the pink handoutGUIcounter.java

Counter.java

• Copy these files, compile them and run the application

• Experiment by changing attributes and see the results

• Code available on EOS~grissom/163/Demos/GUIcounter.java

~grissom/163/Demos/Counter.java


Events & Listeners (12.4)

• When the user performs an action, an event is fired

• Special methods, event handlers, are called automatically by the system

• But only if the component has been registered properly

• For exampleA mother and her son at the park


Buttons (as an example)

• Buttons only generate one kind of event, actionEvent

• An action event requires a special method to be provided

• public void actionPerformed(ActionEvent e)String str = e.getActionCommand();

if (str.equals(“sort”)

• orJComponent = e.getSource();

if (comp == SortButton)


Using GUI Components

• Four Critical Steps1) define as an instance variable2) instantiate the component in the JFrame constructor3) display within a container4) register a listener

• For ExamplesortButton = new JButton (“Sort”);getContentPane().add (sortButton);sortButton.addActionListener(this);


Other events

• Other components generate other events

• See Table 12.5 on page 734

• Which events are fired?mouse moves over a component

window is iconified

JCheckbox is checked


Who is listening?

• There are several approaches to assigning listening responsibility

• Each have strengths and weaknesses

• I prefer to have the Frame listen (Figure 12.16)


GUI Components (12.3)

• There are several GUI components that permit specific kinds of user interaction:JTextField, JTextArea

JButton, JComboBox, JCheckBox

JLabel, JMenu

• Important Methods inherited from JComponentsetBackground(Color c)

setEnabled(boolean)

setSize(width, height)

setVisible(boolean)


JTextField and JTextArea

• A text field displays a single line of text in a GUI

• It can be made editable

• A text area displays multiple lines of text

• A text area automatically has scrollbars on its bottom and right sides if needed

• Sample CodeJTextField text = new JTextField (15);

place on screen

text.setText(“my name”);

String str = text.getText( );


JButton

• A button can be created with or without a label

• An application is usually designed such that when a button is pressed, a particular action occurs

• JButton generates action events

• Sample CodeJButton b = new JButton(“label”);

getContentPane().add(b);

b.addActionListener(this);

• Sample Action ListenerJButton current = (JButton) e.getSource();

if (current == b)

// do something


JComboBox

• A combo box displays a list of choices when pushed

• The user can then scroll through and choose the appropriate option

• JComboBox generates action events and item events

• Sample CodeString[] pets = {“bird”, “cat”, “dog”, “rabbit”};

JCombo petList = new JComboBox(pets);

petList.setSelectedIndex(3);

contentPane().add(petList);

petList.addItemListener(this);

• Sample Item ListenerJComboBox cb = (JComboBox) e.getSource();

String pet = (String) cb.getSelectedItem();


JOptionPanes

• Simple solution for common message boxes that requires little code

• Different styles are providedWARNING_MESSAGE

ERROR_MESSAGE

PLAIN_MESSAGE

• Sample CodeJOptionPane.showMessageDialog (frame, “my specific warning message”, “some

title”, JOptionPane.WARNING_MESSAGE);

JOptionPane.showMessageDialog (frame, “my specific error message”, “some title”, JOptionPane.ERROR_MESSAGE);


JFileChooser (not in book)

• Allows a user to select a file by navigating directories

• The selected filename including the full path are returned

• Programmer chooses between a Save or Open dialog

• Refer to the online documentation for several customized options including file filters

• Sample Codechooser = new JFileChooser( );

int choice = chooser.showOpenDialog(this);

if (choice == JFileChooser.APPROVE_OPTION){

File f = chooser.getSelectedFile( );

// do something with the file

}


Menus (12.4)

• Create pull down menus• They appear in the menu bar• Advanced Options

keyboard shortcuts

cascading menus

adding icons

• Sample code to create a menu// create the menu bar

menuBar = new JMenuBar();

// build a menu

fileMenu = new JMenu(“File”);

quitItem = new JMenuItem(“Quit”);

quitItem.addActionListener(this);

fileMenu.add(quitItem);

// add menu to the bar

menuBar.add(fileMenu);


More Menus

• Menu Items generate action events

• Sample Action Listenerif (e.getSource() == quitItem)

// do something


Class Play

• three GUI componentsGUI 1

GUI 2

GUI 3

• two event listenersclap

double clap

• four methods

• the user


Window Events

• Windows generate a number of events

• the most important for us is the close event

• Create a window adaptor to hide most of the methods

class myWindowHandler extends WindowAdapter{

public void windowClosing(WindowEvent e){

System.exit(0);}

}

• Register this listener from within the GUI constructor

addWindowListener (new myWindowHandler());


Model View Pattern

• Separate GUI front end from the application

• provides flexibility for future interface development

• Viewcreate frames and components

create instance of model

handle events

• Modelmanage data

respond to View requests

should not know anything about the View

• ResponsibilitiesTom and Mary have their own jobs and will be upset if

someone else does it


GUI Design

• Careful design of a graphical user interface is key to a viable software system

• To the user, the user interface is the system

• For each situation, consider which components are best suited and how they should best be arranged

• Group ActivityDesign a VCR display with TV screen, play, stop, ff,

rewind, volume control, channel controls

scott grissom, copyright 2004ch 12: swing slide 1 how do i learn gui development? use these lecture...

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