使用Graphics2D绘制图像

Question

我正在尝试使用java的Graphics2D在屏幕上绘制图像。这是我正在使用的代码。我希望看到一个图像在屏幕上稳定地移动。目前我可以看到图像，但它不会移动，除非我调整窗口的大小，在这种情况下，它确实会移动。我已经勾画出下面的课程。

public class Tester extends JFrame {
private static final long serialVersionUID = -3179467003801103750L;
private Component myComponent;
public static final int ONE_SECOND = 1000;
public static final int FRAMES_PER_SECOND = 20;
private Timer myTimer;
public Tester (Component component, String title) {
super(title);
myComponent = component;
}
public void start () {
myTimer = new Timer(ONE_SECOND / FRAMES_PER_SECOND, new ActionListener() {
@Override
public void actionPerformed (ActionEvent e) {
repaint();
}
});
myTimer.start();
}
@Override
public void paint (Graphics pen) {
if (myComponent != null) {
myComponent.paint(pen);
}
}
}

传递给测试仪的Component对象是以下类：

public class LevelBoard extends Canvas implements ISavable {
private static final long serialVersionUID = -3528519211577278934L;
@Override
public void paint (Graphics pen) {
for (Sprite s : mySprites) {
s.paint((Graphics2D) pen);
}
}
protected void add (Sprite sprite) {
mySprites.add(sprite);
}

我已经确保这个类只有一个我添加的精灵。sprite类大致如下：

public class Sprite {
private Image myImage;
private int myX, myY;
public Sprite () {
URL path = getClass().getResource("/images/Bowser.png");
ImageIcon img = new ImageIcon(path);
myImage = img.getImage();
}
public void update () {
myX += 5;
myY += 5;
}
public void paint (Graphics2D pen) {
update();
pen.drawImage(myImage, myX, myY,null);
}

然而，我在屏幕上只看到了鲍泽的静止图像。除非调整窗户的大小，否则他不会动。我知道Sprite类中的paint(Graphics2D pen)方法是以特定的间隔调用的(因为Tester类中有Timer)。然而，即使x和y位置每次递增5。精灵不会移动。为什么不呢？我该如何修复它？我现在只是想测试我的程序的一些其他功能，所以我真的只需要启动并运行它。我真的不在乎怎么做。

Answer 1

您的代码充满了问题：

1. 不要覆盖JFrame.paint()，尤其是在没有调用super的情况下。设置ContentPane并覆盖其paintComponent()。虽然它看起来很方便，但它通常是一个糟糕的设计，没有必要
2. 不要覆盖JComponent.paint()，而是覆盖JComponent.paintComponent()(并调用super)
3. 使用JLabel显示图像。它要简单得多
4. 不要混合AWT(Canvas)和Swing(JFrame)。坚持摇摆

下面是一个简单的例子，显示了一个Bowser在框架周围移动。(当你缩小帧大小并用帧边界击中图像时，这很有趣；-)

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Random;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.UnsupportedLookAndFeelException;
public class TestAnimation2 {
private static final int NB_OF_IMAGES_PER_SECOND = 50;
private static final int WIDTH = 800;
private static final int HEIGHT = 600;
private Random random = new Random();
private double dx;
private double dy;
private double x = WIDTH / 2;
private double y = HEIGHT / 2;
protected void initUI() throws MalformedURLException {
final JFrame frame = new JFrame(TestAnimation2.class.getSimpleName());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(null);
final JLabel label = new JLabel(new ImageIcon(new URL("http://www.lemondedemario.fr/images/dossier/bowser/bowser.png")));
label.setSize(label.getPreferredSize());
frame.setMinimumSize(label.getPreferredSize());
frame.add(label);
frame.setSize(WIDTH, HEIGHT);
dx = getNextSpeed();
dy = getNextSpeed();
Timer t = new Timer(1000 / NB_OF_IMAGES_PER_SECOND, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
x += dx;
y += dy;
if (x + label.getWidth() > frame.getContentPane().getWidth()) {
x = frame.getContentPane().getWidth() - label.getWidth();
dx = -getNextSpeed();
} else if (x < 0) {
x = 0;
dx = getNextSpeed();
}
if (y + label.getHeight() > frame.getContentPane().getHeight()) {
y = frame.getContentPane().getHeight() - label.getHeight();
dy = -getNextSpeed();
} else if (y < 0) {
y = 0;
dy = getNextSpeed();
}
label.setLocation((int) x, (int) y);
}
});
frame.setVisible(true);
t.start();
}
private double getNextSpeed() {
return 2 * Math.PI * (0.5 + random.nextDouble());
}
public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException,
UnsupportedLookAndFeelException {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
try {
new TestAnimation2().initUI();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
}