ChangeListener未触发

Question

我正在学习更改听众，并希望了解为什么我的编码部分在用户移动滑块时不会使更改侦听器触发。

这是听众。一切都采用相同的方法：

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

以下是添加侦听器的一些代码：

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);

此代码基于上面的代码块，但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

您的代码部分似乎有问题，正如您在showDate()方法的评论中指出的那样，此代码在此代码中完美无缺：

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();
            }
        });
    }
}