WebDeitelCh11_part2_BasicGUI

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BasicGUICo

mponents

Basic GUI Components

Java: How to Program

Chapter 14 (continued)

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BasicGUICo

mponents Basic Java GUI

Focus: Event Handling in Java's Graphical User

Interface

GUIs are event driven

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mponents

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Swing vs. AWT (14.4)

Original (AWT) GUI components - heavyweight:

rely on local platform's windowing system to determinefunctionality and look and feel

Look and feel: a components appearance and the

way in which the user interacts with it.

result: platform-dependent appearance

Swing GUI Components are lightweight:

Written, manipulated and displayed completely in Java

not "weighed down" by platform's GUI capabilities


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mponents Swing vs. AWT (14.4)

You can include Swing and AWT components on the same

GUI. The picture below shows the difference between AWT and

Swing:

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BasicGUIComponents Setting up Event Handling for GUI Component

1. Must create a class that represents the event handler

and implements an appropriate interfaceknown asan event-listener interface.

In Craps.java, the Craps class implemented

Actionlistener and declared the only method for that

interface -> actionPerformed, satisfying this step.

2. Must indicate that an object of the class from Step 1

should be notified when the event occursknown as

registering the event handler. In Craps.java, this step was accomplished (for the roll

Jbutton) by the following:

Roll.addActionListener(this);

The addActionListener argument is an ActionListener object,which in this case is the current instance of the Craps object 5


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Event Registration (14.6)

Consider the following code from Figure 14.9 on the

following slides.Note that class TextFieldFrame extends JFrame but

does not implement ActionListener (contrary to our

Craps.java example).

Instead, class TextFieldHandler implements the

ActionListener interface and therefore defines

actionPerformed.


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BasicGUIComponents Event Registration (14.6)

When you click on a component, it receives focus (cursor

appears in textfield)

When the user presses ENTER while one of the JTextFields or

JPasswordFields has focus, causes the system to generate anActionEvent object

ActionEvent objects contain information about the event that just

occurred, such as:

the event source the text in the text field.

getSource() method returns a reference to the event

source

Line 58 in Fig. 14.9 asks, Is the event source textField1?10


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BasicGUIComponents Event Registration (14.6)

The ActionEvent is processed by an object that implements the

ActionListener interface (in our example: TextFieldHandler) The TextFieldHandler class satisfies #1 in slide 3

But before this can occur, the program must register the

TextFieldHandler object as the event handler for the

JTextFields and the JPasswordField. TextField1.addActionListener(handler);

registers handler(which is of type TextFieldHandler) as

the event handler for the TextField1 component

Satisfies #2 in slide 3

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BasicGUIComponents Key Event Handling

Implementing KeyListener will allow you to create a

dynamic response to users pressing ANY key In our last example, only pressing enter would generate

an event

Must declare the methods:

keyPressed (called when any key is pressed)

keyTyped (called in response to pressing any key

that is not an action key

Action keys:arrows, home, end, page up, page down,any function keyall non-characters

keyReleased (called when any key is released)

Must register with addKeyListener(KeyEvent) method

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Event Handling (14.7-14.8)

Event information is stored in an object that extends

AWTEvent: ActionEvent is the object weve seen in our examples so far


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BasicGUIComponents Event Handling (14.7-14.8)

Javas event handling model is called the delegation event

model: event processing is delegatedto a particular object (the event

listener) within a program

use of delegation allows more than one event of the same type to

be handled by the program (ie., multiple JButton's)

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Java uses Several Types of Event Listeners

actionListeners:

JButtons (command buttons), JTextFields, JPasswordFields

itemListeners:

JCheckBoxs (true/false values),

JToggleButtons (used with toolbars), and

JRadioButtons (on/off values)

JComboBox (drop-down lists)

Each event listener type has a handler:

more than one component of same listener type can be used,

if so, "delegation event model" object (usually an inner class) is

used to parse out program's course of action


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Delegation Event Model and Fancy Buttons (14.9)

14 Container c = getContentPane(); // fig 12.10

15 c.setLayout( new FlowLayout() );

// create buttons

18 plainButton = new JButton( "Plain Button" );

19 c.add( plainButton );

21 Icon bug1 = new ImageIcon( "bug1.gif" );

22 Icon bug2 = new ImageIcon( "bug2.gif" );23 fancyButton = new JButton("Fancy Button",bug1);

24 fancyButton.setRolloverIcon( bug2 );

25 c.add( fancyButton );

// innerclass ButtonHandler for button event handling

29 ButtonHandler handler = new ButtonHandler();

30 fancyButton.addActionListener( handler );

31 plainButton.addActionListener( handler );


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An inner class used for button event handling (14.9)

52 private class ButtonHandler implements

ActionListener {

53 public void actionPerformed( ActionEvent e ){

55 JOptionPane.showMessageDialog( null,

56 "You pressed: " + e.getActionCommand() );

if (e.getActionCommand() == "Plain Button")

doSomethingPlain();

if (e.getActionCommand() == "Fancy Button")

doSomethingFancy();

57 }

}

}

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WebDeitelCh11_part2_BasicGUI