ChangeListener未触发

Question

我正在学习有关change listener的知识，我想知道为什么当用户移动滑块时，我的代码的一部分不会触发change listener。

这是监听程序。所有的方法都是一样的：

ChangeListener lst = new ChangeListener() {
    public void stateChanged(ChangeEvent e) {
        showDate();
    }
};

下面是一些添加侦听器的代码：

m_slDay = new JSlider(JSlider.HORIZONTAL, 1, maxDays,
    m_calendar.get(Calendar.DAY_OF_MONTH));
m_slDay.setPaintLabels(true);
m_slDay.setMajorTickSpacing(5);
m_slDay.setMinorTickSpacing(1);
m_slDay.setPaintTicks(true);

// This line of code seems to work.  
m_slDay.addChangeListener(lst);

p = new JPanel();
p.setBorder(new TitledBorder(new EtchedBorder(), "Day"));
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
p.add(Box.createRigidArea(RIGID_DIMENSION));
p.add(m_slDay);
p.add(Box.createRigidArea(RIGID_DIMENSION));
p1.add(p);

这段代码基于上面的代码块，但是当用户移动滑块时没有任何反应：

m_slDayOfWeek = new JSlider(JSlider.HORIZONTAL, 1, maxDaysOfTheWeek,
    m_calendar.get(Calendar.DAY_OF_WEEK));
m_slDayOfWeek.setPaintLabels(true);
m_slDayOfWeek.setMajorTickSpacing(1);
m_slDayOfWeek.setMinorTickSpacing(1);
m_slDayOfWeek.setPaintTicks(true);

// This one is not working and I'm not sure why it's happening.
m_slDayOfWeek.addChangeListener(lst);

p = new JPanel();
p.setBorder(new TitledBorder(new EtchedBorder(), "Day of Week"));
p.setLayout(new BoxLayout(p, BoxLayout.Y_AXIS));
p.add(Box.createRigidArea(RIGID_DIMENSION));
p.add(m_slDayOfWeek);
p.add(Box.createRigidArea(RIGID_DIMENSION));
p1.add(p);

Answer 1

就像你的showDate()方法中的注释指出的那样，你的代码部分似乎有问题，它在下面的代码中工作得很完美：

import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class SliderChangeEffect extends JFrame
{
    private JSlider slider;
    private int count = 0;
    private ChangeListener changeListener = new ChangeListener()
    {
        public void stateChanged(ChangeEvent ce)
        {
            System.out.println(count++);
        }
    };

    private void createAndDisplayGUI()
    {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationByPlatform(true);

        JPanel contentPane = new JPanel();
        contentPane.setOpaque(true);

        slider = new JSlider(0, 10, 5);
        slider.setMajorTickSpacing(2);
        slider.setMinorTickSpacing(1);
        slider.addChangeListener(changeListener);

        contentPane.add(slider);

        getContentPane().add(contentPane);
        pack();
        setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new SliderChangeEffect().createAndDisplayGUI();
            }
        });
    }
}