我希望这不会出现太多新手问题。我之前没有完成图形样式编程。我的目标是在applet中创建一个弹球广告游戏。但是，我陷入了第一个障碍之一。我的applet没有显示我的Table类（扩展JPanel）的paintComponent方法的结果。我尝试过几个方面，例如我如何加载图像（目前使用双缓冲，但之前我确实使用过mediatracker），看看是否没有任何其他GUI内容可以让绘画发生（因为我想知道它是否正在以某种方式被绘制出来）和其他东西。这个问题困扰了我，我开始怀疑（并希望）它是否是我忽略的小事，如果是的话，那我很抱歉但仍会感激不尽求助，因为我不能在没有先解决这个问题的情况下走得很远。我的弹球（applet）和Table类的代码如下，其他类尚未实现。再一次，我感谢任何帮助。
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;
}
}
答案 0 :(得分：2)
您的表JPanel由其他JPanel覆盖，可以没问题，但您将无法看到覆盖它的不透明组件，特别是tablePanel JPanel。例如，尝试：
tablePanel = new JPanel();
// tablePanel.setBackground(bgColour); //!! removed
tablePanel.setOpaque(false); //!! added
看看会发生什么。
关于此代码的一个无关的问题：
public void init() {
setSize(300, 300);
table = new Table(this);
add(table);
setContentPane(table); // makes our graphical JPanel container the content
为什么要将表对象添加两次，一次添加到JApplet的contentPane，然后再添加作为 JApplet的contentPane？
答案 1 :(得分：1)
运行然后检查此代码＆amp;看看你是否能发现问题的根源。
// <applet code='Pinball' width='300' height='300'></applet>
import java.awt.*;
import java.awt.image.BufferedImage;
import javax.swing.*; // useful for the drawing side, also going to be a JApplet
import javax.imageio.ImageIO;
import java.net.*;
import java.io.IOException;
public class Pinball extends JApplet {
// variables go here
Table table;
// further initialisation of the GUI
public void init() {
table = new Table(this);
setContentPane(table); // makes our graphical JPanel container the content pane for the Applet
}
}
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");
int size = 100;
logo = //loadImage("logo.jpg");
new BufferedImage( size,size, BufferedImage.TYPE_INT_RGB);
Graphics g = logo.getGraphics();
g.setColor(Color.red);
g.fillRect(0,0,size,size);
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(20,20));
// 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.green));
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");
}
@Override
public void paintComponent(Graphics g) {
System.out.println("paintComponent");
super.paintComponent(g);
g.setColor(Color.black);
g.drawImage(logo, 5, 5, 90, 90, this);
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) {
// do NOT ignore exceptions in broken code.
}
return image;
}
}