Java 对象移动 [英] Java object movement
问题描述
我试图让一个圆圈在键盘输入中移动.我根本无法移动对象.有人可以帮我找出问题所在吗?这是我的代码:
I am trying to get a circle to move through the input of a keyboard. I am not able to move the object at all. Can someone help me figure out what is wrong? Here is my code:
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JPanel;
public class AlienInvader extends JPanel implements KeyListener{
Constants constant = new Constants();
public void update() {
constant.x += constant.xvel;
addKeyListener(this);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.MAGENTA);
g.fillOval(constant.x, constant.y, 30, 30);
repaint();
}
@Override
public void keyPressed(KeyEvent e) {
System.out.println(constant.x);
switch(e.getKeyCode()) {
case KeyEvent.VK_LEFT:
constant.xvel = -1;
break;
case KeyEvent.VK_RIGHT:
constant.xvel = 1;
break;
}
}
@Override
public void keyReleased(KeyEvent e) {
switch(e.getKeyCode()) {
case KeyEvent.VK_LEFT:
constant.xvel = -1;
break;
case KeyEvent.VK_RIGHT:
constant.xvel = 1;
break;
}
}
@Override
public void keyTyped(KeyEvent arg0) {
// TODO Auto-generated method stub
}
}
我不确定我做错了什么.我以为是因为我没有调用update方法，但是当我在paintComponent中添加了一个if语句(所以它只调用自己一次)并尝试了它时，我没有运气.
I am not sure what I am doing wrong. I thought it was because I wasn't calling the update method, but when I added a if statement in paintComponent (so it only calls itself once) and tried it, I had no luck.
推荐答案
首先，不要在任何 paintXxx 方法中调用 repaint.绘制方法通常被调用以响应对 repaint 的调用，因此您正在创建一个令人讨厌的、永无止境的、消耗资源的地狱循环.
To start with, don't call repaint within any paintXxx method. Paint methods are typically called in response to a call to repaint, therefore you are creating a nasty, never ending, ever consuming loop of resource hell.
其次，KeyListeners 仅在 1- 注册的组件可聚焦 2- 注册的组件具有焦点时才响应键事件.
Secondly, KeyListeners only respond to key events when 1- The component the are registered to are focusable 2- When the component they are registered to have focus.
在这种情况下，它们是一个糟糕的选择.改用 键绑定
They are a poor choice in this case. Use Key bindings instead
第三，您没有提供 preferredSize 提示供布局管理器使用.在您的情况下，这可能是也可能不是一件坏事，但您的组件可能会以 0x0 的大小布局
Thirdly, you are not providing a preferredSize hint for layout managers to use. This may or may not be a bad thing in your case, but it's possible that you component will be laid out with a size of 0x0
示例
类似......
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
public class MoveCircle {
public static void main(String[] args) {
new MoveCircle();
}
public MoveCircle() {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new TestPane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class TestPane extends JPanel {
private int xDelta = 0;
private int keyPressCount = 0;
private Timer repaintTimer;
private int xPos = 0;
private int radius = 10;
public TestPane() {
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "pressed.left");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "pressed.right");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "released.left");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "released.right");
am.put("pressed.left", new MoveAction(-2, true));
am.put("pressed.right", new MoveAction(2, true));
am.put("released.left", new MoveAction(0, false));
am.put("released.right", new MoveAction(0, false));
repaintTimer = new Timer(40, new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
xPos += xDelta;
if (xPos < 0) {
xPos = 0;
} else if (xPos + radius > getWidth()) {
xPos = getWidth() - radius;
}
repaint();
}
});
repaintTimer.setInitialDelay(0);
repaintTimer.setRepeats(true);
repaintTimer.setCoalesce(true);
}
@Override
public Dimension getPreferredSize() {
return new Dimension(200, 200);
}
@Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.RED);
g2d.drawOval(xPos, 0, radius, radius);
g2d.dispose();
}
public class MoveAction extends AbstractAction {
private int direction;
private boolean keyDown;
public MoveAction(int direction, boolean down) {
this.direction = direction;
keyDown = down;
}
@Override
public void actionPerformed(ActionEvent e) {
xDelta = direction;
if (keyDown) {
if (!repaintTimer.isRunning()) {
repaintTimer.start();
}
} else {
repaintTimer.stop();
}
}
}
}
}
例如...
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