JApplet问题中的Java绘制图形

Question

我希望这不会显得太新手问题。我以前没有做过图形风格的编程。我的目标是在小程序中创建弹球广告游戏。但是，我遇到了第一个障碍。我的小程序不显示来 self 的 Table 类(它扩展了 JPanel)的 paintComponent 方法的结果。我已经尝试了几件事，比如我如何加载图像(目前使用双缓冲，但我之前确实使用过 mediatracker)，看看是否没有任何其他 GUI 东西会允许绘画发生(因为我想知道它是否正在以某种方式绘制在下面)和其他东西。这个问题让我很困惑，我开始怀疑(并希望)它是否是我忽略的小问题，如果是，那么我很抱歉，但仍然会很感激你的帮助，因为我不能去远没有先解决这个问题。我的 Pinball(小程序)和 Table 类的代码如下，其他类尚未实现。我再次感谢任何帮助。

import javax.swing.*; // useful for the drawing side, also going to be a JApplet
import java.awt.*;
import java.net.*;

public class Pinball extends JApplet {
    // variables go here
    Table table;

    // further initialisation of the GUI
    public void init() {
                        setSize(300, 300);
                table = new Table(this);
                add(table);
                                setContentPane(table); // makes our graphical JPanel container the content pane for the Applet
                // createGUI(); // this has been moved onto the table class
            }

    public void stop() {

    }

}

现在是 Table 类:

import java.awt.*; // needed for old style graphics stuff
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import javax.swing.*; // gives us swing stuff
import java.io.IOException;
import java.net.*; // useful for anything using URLs

public class Table extends JPanel {
// attributes go here
    Pinball pb;
    Color bgColour;
    JPanel eastPanel;
    JPanel logoPanel;
    JPanel livesPanel;
    JPanel scorePanel;
    JPanel tablePanel;
    JPanel scrollTextPanel;
        Image logo;

    // constructor goes here
public Table(Pinball pb) {
setPreferredSize(new Dimension(300, 300));
    this.pb = pb;
    // this is not needed anymore, with the new loadImage class down the bottom
//  Toolkit tk = Toolkit.getDefaultToolkit(); // needed to get images
//  logo = tk.getImage(base + "images/logo.jpg");
        logo = loadImage("logo.jpg");
     createGUI();
        }

        // public methods go here
        // all GUI creation stuff goes here
        public void createGUI() {
            /* allows the three parts (top, middle and right) 
             * to be made through (north, center and right) */
                    setLayout(new BorderLayout());
                    // setting the background colour
                    bgColour = new Color(190, 186, 221); // makes the sky blue colour for the background.
                    setBackground(bgColour);
                                                        // now putting a panel for the east side
                    eastPanel = new JPanel();
                    eastPanel.setBackground(bgColour);
                    eastPanel.setLayout(new BorderLayout(8, 8));
                    eastPanel.setPreferredSize(new Dimension(100, 280));
                                    logoPanel = new JPanel();
    logoPanel.setBackground(Color.WHITE);
    logoPanel.setPreferredSize(new Dimension(100, 100));
    logoPanel.setBorder(BorderFactory.createMatteBorder(5, 5, 5, 5, Color.white));
    //JLabel label1 = new JLabel("Logos go here");
    //logoPanel.add(label1);
    eastPanel.add(logoPanel, "North");
    livesPanel = new JPanel();
    livesPanel.setBackground(Color.WHITE);
    livesPanel.setPreferredSize(new Dimension(100, 100));
    JLabel label2 = new JLabel("Lives go here");
    livesPanel.add(label2);
    eastPanel.add(livesPanel, "Center");
    scorePanel = new JPanel();
    scorePanel.setBackground(Color.WHITE);
    scorePanel.setPreferredSize(new Dimension(100, 80));
    JLabel label3 = new JLabel("Scores go here");
    scorePanel.add(label3);
    eastPanel.add(scorePanel, "South");
add(eastPanel, "East");
    tablePanel = new JPanel();
    tablePanel.setBackground(bgColour);
    tablePanel.setPreferredSize(new Dimension(200, 280));
    add(tablePanel, "Center");
    scrollTextPanel = new JPanel();
    scrollTextPanel.setPreferredSize(new Dimension(300, 20));
    scrollTextPanel.setBackground(Color.WHITE);
    scrollTextPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
    add(scrollTextPanel, "North");
    // repaint();
                        }

        public void paintComponent(Graphics g) {
            super.paintComponent(g);
        g.drawImage(logo, 5, 5, 90, 90, null);
        g.drawLine(0, 0, 300, 300); // for testing, does not work
              }

        // a little useful method for handling loading of images and stuff
        public BufferedImage loadImage(String filename) {
        BufferedImage image = null;
        try {
               URL url = new URL(pb.getCodeBase(), "images/" + filename);
               image = ImageIO.read(url);
            } catch (IOException e) {
            }
    return image;
        }

}

Answer 1

您的 Table JPanel 被其他 JPanel 覆盖，这没问题，但您将无法透过覆盖它的不透明组件看到它，尤其是 tablePanel JPanel。例如，尝试:

  tablePanel = new JPanel();
  // tablePanel.setBackground(bgColour); //!! removed
  tablePanel.setOpaque(false); //!! added

然后看看会发生什么。

这里有一个与此代码无关的问题:

   public void init() {
      setSize(300, 300);
      table = new Table(this);
      add(table);
      setContentPane(table); // makes our graphical JPanel container the content

为什么要两次添加表格 Table 对象，一次添加到 JApplet 的 contentPane，然后 添加到 JApplet 的 contentPane？