java - JLabel 尝试拖动时消失

我正在构建一个应用程序，它将标签放置在用户单击面板 (jpanel2) 的位置，并允许它移动放置的标签。

我可以成功放置标签，但无法移动其中任何一个。事实上，当我尝试拖动标签时，在我所有的尝试中它都会消失。我也尝试在 jPanel2 和 JFrame 中调用重绘，但仍然没有成功。

JPanel 2 没有布局(自由设计)，因为想要将标签准确地放置在鼠标单击的位置。

更新

这是问题发生的一个最小示例。我无法减少面板的数量，因为我需要在屏幕上放置更多控件(例如 jtable、菜单和工具栏)。

public class Example extends javax.swing.JFrame {

    static int count = 0;

    public Example() {
        initComponents();
    }

    @SuppressWarnings("unchecked")                 
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();
        jPanel2 = new javax.swing.JPanel();
        jPanel3 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setPreferredSize(new java.awt.Dimension(600, 600));

        jPanel2.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseClicked(java.awt.event.MouseEvent evt) {
                jPanel2MouseClicked(evt);
            }
        });

        jPanel3.setMinimumSize(new java.awt.Dimension(0, 0));
        jPanel3.setLayout(new java.awt.BorderLayout());
        jPanel3.add(jLabel1, java.awt.BorderLayout.CENTER);

        javax.swing.GroupLayout jPanel2Layout = new javax.swing.GroupLayout(jPanel2);
        jPanel2.setLayout(jPanel2Layout);
        jPanel2Layout.setHorizontalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        jPanel2Layout.setVerticalGroup(
            jPanel2Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel3, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(jPanel1Layout.createSequentialGroup()
                .addComponent(jPanel2, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );

        getContentPane().add(jPanel1, java.awt.BorderLayout.CENTER);

        pack();
    }// </editor-fold>                        

    private void jPanel2MouseClicked(java.awt.event.MouseEvent evt) {                                     

        count++;
        addAnnotation(String.valueOf(count), evt.getX(), evt.getY());
    }                                    

    private void addAnnotation(String labelStr, int x, int y) {

        final JLabel label = new JLabel(labelStr);
        jPanel2.add(label);
        label.setLocation(x, y);

        System.out.println("Adding to " + x + " " + y);

        label.setSize(20, 20);
        label.setBackground(Color.WHITE);
        label.setOpaque(true);
        label.setBorder(new LineBorder(Color.BLACK, 1, false));
        label.setHorizontalAlignment(SwingConstants.CENTER);
        label.setVisible(true);
        label.setForeground(Color.BLACK);

        label.addMouseMotionListener(new MouseMotionListener() {

            @Override
            public void mouseDragged(MouseEvent e) {
                Component c = e.getComponent();

                int moveToX = c.getX() + e.getX();
                int moveToY = c.getY() + e.getY();
                c.setLocation(moveToX, moveToY);
                System.out.println("Moving to " + moveToX + " " + moveToY);
            }

            @Override
            public void mouseMoved(MouseEvent e) {
            }
        });
    }

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(Example.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Example().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JPanel jPanel2;
    private javax.swing.JPanel jPanel3;
    // End of variables declaration                   
    }

最佳答案

如果你要使用 GUI Builder 来制作程序，你需要做的就是将面板的布局设置为空。然后，当您向面板添加标签时，需要为其设置边界。下面是如何实现此目的的示例。

首先我添加了一个空白JPanel到框架形式(jPanel1)。我将其扩展到框架的大小。
然后我在构造函数中添加了所有其余代码。我添加了JLabel到jPanel然后revalidate()和repaint() jPanel1 .
然后我添加了 MouseMotionListener

这是我添加的唯一代码。全部在构造函数中。除了pX和pY变量作为类成员

int pX, pY;
public NewJFrame() {
    initComponents();
    jPanel1.setLayout(null);
    final JLabel label = new JLabel();
    label.setHorizontalAlignment(JLabel.CENTER);
    label.setBounds(50, 50, 50, 50);
    label.setBorder(new LineBorder(Color.black, 3));
    label.setText("Hello");

    label.addMouseMotionListener(new MouseMotionAdapter(){
        public void mouseDragged(MouseEvent me) {
            label.setLocation(label.getLocation().x + me.getX() - pX, 
                        label.getLocation().y + me.getY() - pY);
            jPanel1.revalidate();
            jPanel1.repaint();
        }
    });
    label.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent me) {
                // Get x,y and store them
                pX = me.getX();
                pY = me.getY();
            }
        });

    jPanel1.add(label);
    jPanel1.revalidate();
    jPanel1.repaint();
}

enter image description here

这是完整的程序

import java.awt.Color;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import javax.swing.JLabel;
import javax.swing.border.LineBorder;

public class NewJFrame extends javax.swing.JFrame {

    int pX, pY;
    public NewJFrame() {
        initComponents();
        jPanel1.setLayout(null);
        final JLabel label = new JLabel();
        label.setHorizontalAlignment(JLabel.CENTER);
        label.setBounds(50, 50, 50, 50);
        label.setBorder(new LineBorder(Color.black, 3));
        label.setText("Hello");

        label.addMouseMotionListener(new MouseMotionAdapter(){
            public void mouseDragged(MouseEvent me) {
                label.setLocation(label.getLocation().x + me.getX() - pX, 
                            label.getLocation().y + me.getY() - pY);
                jPanel1.revalidate();
                jPanel1.repaint();
            }
        });
        label.addMouseListener(new MouseAdapter() {
                public void mousePressed(MouseEvent me) {
                    // Get x,y and store them
                    pX = me.getX();
                    pY = me.getY();
                }
            });

        jPanel1.add(label);
        jPanel1.revalidate();
        jPanel1.repaint();
    }

    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jPanel1 = new javax.swing.JPanel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
        jPanel1.setLayout(jPanel1Layout);
        jPanel1Layout.setHorizontalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 388, Short.MAX_VALUE)
        );
        jPanel1Layout.setVerticalGroup(
            jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGap(0, 288, Short.MAX_VALUE)
        );

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addContainerGap())
        );

        pack();
    }// </editor-fold>                        

    public static void main(String args[]) {
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JPanel jPanel1;
    // End of variables declaration                   
}

关于java - JLabel 尝试拖动时消失，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/21217368/

java - JLabel 尝试拖动时消失

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