java - JLabel 无法使用鼠标运动监听器正确移动，为什么？

Question

每当我拖动鼠标时，我都需要相应地移动 JLabel。
为什么拖动时显示多个 JLabel 而没有在正确的位置显示组件？

public class Mover extends JFrame 
{

private JPanel jPanel;
private JLabel jLabel1;
private JLabel jLabel2;
private int myXX = 0;
private int myYY = 0;

public Mover() {
    setSize(500, 500);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    jPanel = new JPanel(null);
    jLabel1 = new JLabel("label one");
    jLabel2 = new JLabel("label two");

    jLabel1.setBounds(100, 100, 100, 100);
    jLabel2.setBounds(100, 100, 100, 100);
    jLabel1.addMouseMotionListener(new MouseMotionListener() {

        @Override
        public void mouseMoved(MouseEvent e) {
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            System.out.println("Label One");
            myXX = e.getX() - (jLabel1.getWidth() / 2);
            myYY = e.getY() - (jLabel1.getHeight() / 2);
            jLabel1.setLocation(myXX, myYY);
            repaint();
        }
    });
    jLabel2.addMouseMotionListener(new MouseMotionListener() {

        @Override
        public void mouseMoved(MouseEvent e) {
        }

        @Override
        public void mouseDragged(MouseEvent e) {
            System.out.println("Label Two");

            myXX = e.getX() - (jLabel2.getWidth() / 2);
            myYY = e.getY() - (jLabel2.getHeight() / 2);
            jLabel2.setLocation(myXX, myYY);
            repaint();
        }
    });
    jPanel.add(jLabel1);
    jPanel.add(jLabel2);
    add(jPanel);
    repaint();
    revalidate();
    setVisible(true);
}

public static void main(String args[]) {
    new Mover();
}
}

这个问题有完美的解决办法吗？
显然提前致谢。

Answer 1

MouseEvent 信息与生成事件的组件(在本例中为标签)相关。

这意味着0x0实际上是标签的左上角。您需要将事件的点信息转换为其父上下文，例如...

Point p = e.getPoint();
p = SwingUtilities.convertPoint(e.getComponent(), p, e.getComponent().getParent());

您也不需要创建 myXX 或 myYY 实例字段，因为它们只真正具有驱动它们的鼠标事件的上下文。

您还应该看看Initial Threads并确保您在事件调度线程的上下文中启动您的程序...

您也不需要为每个组件创建单独的监听器，只需巧妙地使用 MouseEvent 中的可用信息，您就可以为所有组件使用单个监听器并减少代码重复...

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Point;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Mover extends JFrame {

    private JPanel jPanel;
    private JLabel jLabel1;
    private JLabel jLabel2;

    public Mover() {
        setSize(500, 500);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        jPanel = new JPanel(null);
        jLabel1 = new JLabel("label one");
        jLabel2 = new JLabel("label two");

        jLabel1.setBounds(100, 100, 100, 100);
        jLabel2.setBounds(100, 100, 100, 100);

        MouseMotionListener mover = new MouseMotionListener() {

            @Override
            public void mouseMoved(MouseEvent e) {
            }

            @Override
            public void mouseDragged(MouseEvent e) {
                System.out.println("Label One");

                Component child = e.getComponent();
                Point p = e.getPoint();
                p = SwingUtilities.convertPoint(e.getComponent(), p, e.getComponent().getParent());

                int myXX = p.x - (child.getWidth() / 2);
                int myYY = p.y - (child.getHeight() / 2);
                child.setLocation(myXX, myYY);
                repaint();
            }
        };

        jLabel1.addMouseMotionListener(mover);
        jLabel2.addMouseMotionListener(mover);

        jPanel.add(jLabel1);
        jPanel.add(jLabel2);
        add(jPanel);
        setVisible(true);
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                new Mover();
            }
        });
    }
}

如果我没有指出直接从像 JFrame 这样的顶级容器扩展是不好的做法，并且会将您锁定在一次性容器中，那么我就会对您造成伤害。如果您愿意的话，将来很难重新使用该容器或将其添加到其他容器...此外，您并没有真正向其添加任何功能...