Java：paintComponent沒有被調用

Question

我的完整代碼（拖放代碼）（只有類Surface和draw（）函數是手動的）：

import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
import javax.swing.text.DefaultFormatter;


class Surface extends JPanel {
int x1,y1,x2,y2;

public Surface(){

}

public Surface(int x1,int y1,int x2,int y2){
    this.x1=x1;
    this.y1=y1;
    this.x2=x2;
    this.y2=y2;
}

private void doDrawing(Graphics g) { // 3
    Graphics2D g2d = (Graphics2D) g;

    g2d.drawLine(x1, y1, x2, y2);
}


@Override
public void paintComponent(Graphics g) { // 2
    super.paintComponent(g);
    doDrawing(g);
}
}
public class NewJFrame extends JFrame {

int x1,y1,x2,y2;

/**
 * Creates new form NewJFrame
 */
public NewJFrame() {
    initComponents();
    draw();
}

private void draw(){
    xSpinner.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            x1=(int) ((JSpinner)e.getSource()).getValue();
            add(new Surface(x1,y1,x2,y2));

        }
    });
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    controlPanel = new javax.swing.JPanel();
    xSpinner = new javax.swing.JSpinner();
    ySpinner = new javax.swing.JSpinner();
    widthSpinner = new javax.swing.JSpinner();
    heightSpinner = new javax.swing.JSpinner();
    xLabel = new javax.swing.JLabel();
    yLabel = new javax.swing.JLabel();
    widthLabel = new javax.swing.JLabel();
    heightLabel = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    xLabel.setText("x");

    yLabel.setText("y");

    widthLabel.setText("width");

    heightLabel.setText("height");

    javax.swing.GroupLayout controlPanelLayout = new javax.swing.GroupLayout(controlPanel);
    controlPanel.setLayout(controlPanelLayout);
    controlPanelLayout.setHorizontalGroup(
        controlPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, controlPanelLayout.createSequentialGroup()
            .addGap(36, 36, 36)
            .addComponent(xLabel, javax.swing.GroupLayout.PREFERRED_SIZE, 6, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(xSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(21, 21, 21)
            .addComponent(yLabel, javax.swing.GroupLayout.PREFERRED_SIZE, 6, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(ySpinner, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 63, Short.MAX_VALUE)
            .addComponent(widthLabel)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(widthSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(31, 31, 31)
            .addComponent(heightLabel)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(heightSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, 40, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(17, 17, 17))
    );
    controlPanelLayout.setVerticalGroup(
        controlPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(controlPanelLayout.createSequentialGroup()
            .addGap(22, 22, 22)
            .addGroup(controlPanelLayout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(ySpinner, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(widthSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(xLabel)
                .addComponent(yLabel)
                .addComponent(widthLabel)
                .addComponent(heightLabel)
                .addComponent(xSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(heightSpinner, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addContainerGap(258, Short.MAX_VALUE))
    );

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

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

/**
 * @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(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 controlPanel;
private javax.swing.JLabel heightLabel;
private javax.swing.JSpinner heightSpinner;
private javax.swing.JLabel widthLabel;
private javax.swing.JSpinner widthSpinner;
private javax.swing.JLabel xLabel;
private javax.swing.JSpinner xSpinner;
private javax.swing.JLabel yLabel;
private javax.swing.JSpinner ySpinner;
// End of variables declaration                   
}

我正在嘗試從微調器獲得x，y值

private void draw(){
    xSpinner.addChangeListener(new ChangeListener() {
        @Override
        public void stateChanged(ChangeEvent e) {
            x1=(int) ((JSpinner)e.getSource()).getValue();
            add(new Surface(x1,y1,x2,y2));

        }
    });
}

但是似乎未調用Surface類中的paintComponent函數。
請幫忙

Answer 1

問題：

• 您的controlPane使用的是GroupLayout，該布局在中途添加新組件時效果不佳
• 您甚至不應該在ChangeListener中添加新組件，因為這沒有任何意義。 當您要做的只是更改繪制的內容時，為什么要不斷添加新的JPanels？ 而是在GUI創建時添加Surface JPanel，並在ChangeListener中更改x1，y1，x2，y2字段並對其調用repaint() 。

就我自己而言，我將擺脫所有Windows構建器生成的代碼，而只需將Surface作為GUI的中央JPanel。 我將創建另一個包含所有內容的JPanel，為其提供BorderLayout，向其添加單個 Surface實例BorderLayout.CENTER，然后在ChangeListener中，更改此Surface的狀態並對其進行重繪。

Answer 2

我已經解決了 我忘了設置Surface（JPanel）的大小和位置