自定义事件与监听器
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自定义事件与监听器
程序运行图：
//运行方法：java chen.ItemChooser$Demo one two three four fiev
package chen;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.border.*;
import java.util.*;
/**
* This class is a Swing component that presents a choice to the user. It
* allows the choice to be presented in a JList, in a JComboBox, or with a
* bordered group of JRadioButton components. Additionally, it displays the
* name of the choice with a JLabel. It allows an arbitrary value to be
* associated with each possible choice. Note that this component only allows
* one item to be selected at a time. Multiple selections are not supported.
**/
public class ItemChooser extends JPanel {
// These fields hold property values for this component
String name; // The overall name of the choice
String[] labels; // The text for each choice option
Object[] values; // Arbitrary values associated with each option
int selection; // The selected choice
int presentation; // How the choice is presented
// These are the legal values for the presentation field
public static final int LIST = 1;
public static final int COMBOBOX = 2;
public static final int RADIOBUTTONS = 3;
// These components are used for each of the 3 possible presentations
JList list; // One type of presentation
JComboBox combobox; // Another type of presentation
JRadioButton[] radiobuttons; // Yet another type
// The list of objects that are interested in our state
ArrayList listeners = new ArrayList();
// The constructor method sets everything up
public ItemChooser(String name, String[] labels, Object[] values,
int defaultSelection, int presentation)
{
this.name = name;
this.labels = labels;
this.values = values;
this.selection = defaultSelection;
this.presentation = presentation;
// If no values were supplied, use the labels
if (values == null) this.values = labels;
// Now create content and event handlers based on presentation type
switch(presentation) {
case LIST: initList(); break;
case COMBOBOX: initComboBox(); break;
case RADIOBUTTONS: initRadioButtons(); break;
}
}
// Initialization for JList presentation
void initList() {
list = new JList(labels); // Create the list
list.setSelectedIndex(selection); // Set initial state
// Handle state changes
list.addListSelectionListener(new ListSelectionListener() {
public void valueChanged(ListSelectionEvent e) {
ItemChooser.this.select(list.getSelectedIndex());
}
});
// Lay out list and name label vertically
this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS)); // vertical
this.add(new JLabel(name)); // Display choice name
this.add(new JScrollPane(list)); // Add the JList
}
// Initialization for JComboBox presentation
void initComboBox() {
combobox = new JComboBox(labels); // Create the combo box
combobox.setSelectedIndex(selection); // Set initial state
// Handle changes to the state
combobox.addItemListener(new ItemListener() {
public void itemStateChanged(ItemEvent e) {
ItemChooser.this.select(combobox.getSelectedIndex());
}
});
// Lay out combo box and name label horizontally
this.setLayout(new BoxLayout(this, BoxLayout.X_AXIS));
this.add(new JLabel(name));
this.add(combobox);
}
// Initialization for JRadioButton presentation
void initRadioButtons() {
// Create an array of mutually exclusive radio buttons
radiobuttons = new JRadioButton[labels.length]; // the array
ButtonGroup radioButtonGroup = new ButtonGroup(); // used for exclusion
ChangeListener listener = new ChangeListener() { // A shared listener
public void stateChanged(ChangeEvent e) {
JRadioButton b = (JRadioButton)e.getSource();
if (b.isSelected()) {
// If we received this event because a button was
// selected, then loop through the list of buttons to
// figure out the index of the selected one.
for(int i = 0; i < radiobuttons.length; i++) {
if (radiobuttons[i] == b) {
ItemChooser.this.select(i);
return;
}
}
}
}
};
// Display the choice name in a border around the buttons
this.setBorder(new TitledBorder(new EtchedBorder(), name));
this.setLayout(new BoxLayout(this, BoxLayout.Y_AXIS));
// Create the buttons, add them to the button group, and specify
// the event listener for each one.
for(int i = 0; i < labels.length; i++) {
radiobuttons[i] = new JRadioButton(labels[i]);
if (i == selection) radiobuttons[i].setSelected(true);
radiobuttons[i].addChangeListener(listener);
radioButtonGroup.add(radiobuttons[i]);
this.add(radiobuttons[i]);
}
}
// These simple property accessor methods just return field values
// These are read-only properties. The values are set by the constructor
// and may not be changed.
public String getName() { return name; }
public int getPresentation() { return presentation; }
public String[] getLabels() { return labels; }
public Object[] getValues() { return values; }
/** Return the index of the selected item */
public int getSelectedIndex() { return selection; }
/** Return the object associated with the selected item */
public Object getSelectedValue() { return values[selection]; }
/**
* Set the selected item by specifying its index. Calling this
* method changes the on-screen display but does not generate events.
**/
public void setSelectedIndex(int selection) {
switch(presentation) {
case LIST: list.setSelectedIndex(selection); break;
case COMBOBOX: combobox.setSelectedIndex(selection); break;
case RADIOBUTTONS: radiobuttons[selection].setSelected(true); break;
}
this.selection = selection;
}
/**
* This internal method is called when the selection changes. It stores
* the new selected index, and fires events to any registered listeners.
* The event listeners registered on the JList, JComboBox, or JRadioButtons
* all call this method.
**/
protected void select(int selection) {
this.selection = selection; // Store the new selected index
if (!listeners.isEmpty()) { // If there are any listeners registered
// Create an event object to describe the selection
ItemChooser.Event e =new ItemChooser.Event(this, selection, values[selection]);
// Loop through the listeners using an Iterator
for(Iterator i = listeners.iterator(); i.hasNext();) {
ItemChooser.Listener l = (ItemChooser.Listener)i.next();
l.itemChosen(e); // Notify each listener of the selection
}
}
}
// These methods are for event listener registration and deregistration
public void addItemChooserListener(ItemChooser.Listener l) {
listeners.add(l);
}
public void removeItemChooserListener(ItemChooser.Listener l) {
listeners.remove(l);
}
/**
* This inner class defines the event type generated by ItemChooser objects
* The inner class name is Event, so the full name is ItemChooser.Event
**/
public static class Event extends java.util.EventObject {
int selectedIndex; // index of the selected item
Object selectedValue; // the value associated with it
public Event(ItemChooser source,int selectedIndex, Object selectedValue) {
super(source);
this.selectedIndex = selectedIndex;
this.selectedValue = selectedValue;
}
public ItemChooser getItemChooser() { return (ItemChooser)getSource();}
public int getSelectedIndex() { return selectedIndex; }
public Object getSelectedValue() { return selectedValue; }
}
/**
* This inner interface must be implemented by any object that wants to be
* notified when the current selection in a ItemChooser component changes.
**/
public interface Listener extends java.util.EventListener {
public void itemChosen(ItemChooser.Event e);
}
/**
* This inner class is a simple demonstration of the ItemChooser component
* It uses command-line arguments as ItemChooser labels and values.
**/
public static class Demo {
public static void main(String[] args) {
// Create a window, arrange to handle close requests
final JFrame frame = new JFrame("ItemChooser Demo");
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {System.exit(0);}
});
// A "message line" to display results in
final JLabel msgline = new JLabel(" ");
// Create a panel holding three ItemChooser components
JPanel chooserPanel = new JPanel();
final ItemChooser c1 = new ItemChooser("Choice #1", args, null, 0,ItemChooser.LIST);
final ItemChooser c2 = new ItemChooser("Choice #2", args, null, 0,ItemChooser.COMBOBOX);
final ItemChooser c3 = new ItemChooser("Choice #3", args, null,
0,ItemChooser.RADIOBUTTONS);
// An event listener that displays changes on the message line
ItemChooser.Listener l = new ItemChooser.Listener() {
public void itemChosen(ItemChooser.Event e) {
msgline.setText(e.getItemChooser().getName() + ": " +
e.getSelectedIndex() + ": " +
e.getSelectedValue());
}
};
c1.addItemChooserListener(l);
c2.addItemChooserListener(l);
c3.addItemChooserListener(l);
// Instead of tracking every change with a ItemChooser.Listener,
// applications can also just query the current state when
// they need it. Heres a button that does that.
JButton report = new JButton("Report");
report.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
// Note the use of multi-line italic HTML text
// with the JOptionPane message dialog box.
String msg = "<html><i>" +
c1.getName() + ": " + c1.getSelectedValue() + "<br>"+
c2.getName() + ": " + c2.getSelectedValue() + "<br>"+
c3.getName() + ": " + c3.getSelectedValue() + "</i>";
JOptionPane.showMessageDialog(frame, msg);
}
});
// Add the 3 ItemChooser objects, and the Button to the panel
chooserPanel.add(c1);
chooserPanel.add(c2);
chooserPanel.add(c3);
chooserPanel.add(report);
// Add the panel and the message line to the window
Container contentPane = frame.getContentPane();
contentPane.add(chooserPanel, BorderLayout.CENTER);
contentPane.add(msgline, BorderLayout.SOUTH);
// Set the window size and pop it up.
frame.pack();
frame.show();
}
}
}
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