Swing ItemListener介面

處理ItemEvent的類應該實現此介面。該類的物件必須使用元件註冊。可以使用addItemListener()方法註冊該物件。發生操作事件時，將呼叫該物件的itemStateChanged方法。

介面宣告

以下是java.awt.event.ItemListener介面的宣告 -

public interface ItemListener
   extends EventListener

介面方法

方法繼承

此介面從以下介面繼承方法 -

• java.awt.EventListener

ItemListener範例

使用編輯器建立以下Java程式：ItemListenerDemo.java -

package com.yiibai.swing.listener;

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ItemListenerDemo {
    private JFrame mainFrame;
    private JLabel headerLabel;
    private JLabel statusLabel;
    private JPanel controlPanel;

    public ItemListenerDemo() {
        prepareGUI();
    }

    public static void main(String[] args) {
        ItemListenerDemo swingListenerDemo = new ItemListenerDemo();
        swingListenerDemo.showItemListenerDemo();
    }

    private void prepareGUI() {
        mainFrame = new JFrame("Java Swing範例(tw511.com)");
        mainFrame.setSize(400, 400);
        mainFrame.setLayout(new GridLayout(3, 1));

        headerLabel = new JLabel("", JLabel.CENTER);
        statusLabel = new JLabel("", JLabel.CENTER);
        statusLabel.setSize(350, 100);

        mainFrame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent windowEvent) {
                System.exit(0);
            }
        });
        controlPanel = new JPanel();
        controlPanel.setLayout(new FlowLayout());

        mainFrame.add(headerLabel);
        mainFrame.add(controlPanel);
        mainFrame.add(statusLabel);
        mainFrame.setVisible(true);
    }

    private void showItemListenerDemo() {
        headerLabel.setText("Listener in action: ItemListener");
        JCheckBox chkJava = new JCheckBox("Java/Swing");
        JCheckBox chkPy = new JCheckBox("Python");
        JCheckBox chkRuby = new JCheckBox("Ruby");

        chkJava.addItemListener(new CustomItemListener());
        chkPy.addItemListener(new CustomItemListener());
        chkRuby.addItemListener(new CustomItemListener());

        controlPanel.add(chkJava);
        controlPanel.add(chkPy);
        controlPanel.add(chkRuby);
        mainFrame.setVisible(true);
    }

    class CustomItemListener implements ItemListener {
        public void itemStateChanged(ItemEvent e) {
            statusLabel.setText(((JCheckBox) e.getItem()).getText() + " Checkbox: "
                    + (e.getStateChange() == 1 ? "checked" : "unchecked"));
        }
    }
}

執行上面範例程式碼，得到下結果：