我以为我会尝试编写一个可以画一个球的程序，当按下箭头键时，会按照按下的方向在屏幕上移动球。首先，我开始尝试制作一个只能进行“向上”箭头键动作的程序。
我已经四处寻找解决方案，而且无法弄清楚这段代码有什么问题。我不知道我的输入和动作映射是否有问题（即，程序识别按键的问题），或者JComponent和JFrame类如何在摇摆中工作时出现问题。我想也许问题可能也是焦点;我真的不知道如何判断组件何时具有焦点。我认为键已经设置为CNTRL + Y而不是现在，只是因为在某些时候我认为可能是我的字符串在输入地图制作者中指定向上箭头的问题。
在这一点上，我很沮丧，我只是试图让那个该死的东西做某事，所以我使用的输入地图比我们需要的更多。
代码如下，它很短，格式可怕（对不起）：
import java.util.*;
import java.awt.*;
import java.awt.geom.*;
import java.awt.event.*;
import javax.swing.*;
class BallMover
{
public static void main(String[] args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
BallFrame frame = new BallFrame();
}
});
}
}
class BallFrame extends JFrame
{
private static final int DEFAULT_WIDTH = 500;
private static final int DEFAULT_HEIGHT = 500;
private BallComponent comp;
public BallFrame()
{
super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
super.setSize(this.DEFAULT_WIDTH, this.DEFAULT_HEIGHT);
super.setResizable(false);
super.add(new BallComponent());
super.setVisible(true);
super.setFocusable(true);
}
}
class BallComponent extends JComponent
{
private Ellipse2D.Double ellipse;
private double x = 225;
private double y = 225;
private ActionPress actionPress;
public BallComponent()
{
super();
super.setFocusable(true);
InputMap imap1 = this.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp1");
InputMap imap2 = this.getInputMap(JComponent.WHEN_FOCUSED);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp2");
InputMap imap3 = this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp3");
ActionMap amap = this.getActionMap();
amap.put("keyUp1", actionPress);
amap.put("keyUp2", actionPress);
amap.put("keyUp3", actionPress);
}
public void paintComponent(Graphics g)
{
super.repaint(); // clear component //
Graphics2D g2d = (Graphics2D)g;
this.ellipse = new Ellipse2D.Double(x, y, 50, 50);
g2d.fill(this.ellipse);
}
private class ActionPress extends AbstractAction
{
public void actionPerformed(ActionEvent event)
{
y = y + 10;
ellipse = new Ellipse2D.Double(x, y, 50, 50);
repaint();
}
}
}
答案 0 :(得分：2)
似乎您从未初始化actionPress - 尝试将此添加到您的BallComponent构造函数中：
actionPress = new ActionPress();
即，你的构造函数看起来像这样
public BallComponent()
{
super();
super.setFocusable(true);
InputMap imap1 = this.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp1");
InputMap imap2 = this.getInputMap(JComponent.WHEN_FOCUSED);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp2");
InputMap imap3 = this.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
imap1.put(KeyStroke.getKeyStroke("ctrl Y"), "keyUp3");
actionPress = new ActionPress();
ActionMap amap = this.getActionMap();
amap.put("keyUp1", actionPress);
amap.put("keyUp2", actionPress);
amap.put("keyUp3", actionPress);
}
答案 1 :(得分：2)
您可以使用KeyboardFocusManager收听箭头键的击键并更新球的位置。这是重写的代码：
class BallFrame extends JFrame {
private static final int DEFAULT_WIDTH = 500;
private static final int DEFAULT_HEIGHT = 500;
final BallComponent ball = new BallComponent();
public BallFrame() {
super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
super.setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
super.setResizable(false);
super.add(ball);
super.setVisible(true);
KeyboardFocusManager.getCurrentKeyboardFocusManager()
.addKeyEventDispatcher(new KeyEventDispatcher() {
@Override
public boolean dispatchKeyEvent(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_UP)
ball.move(0, -10);
if (e.getKeyCode() == KeyEvent.VK_RIGHT)
ball.move(10, 0);
if (e.getKeyCode() == KeyEvent.VK_LEFT)
ball.move(-10, 0);
if (e.getKeyCode() == KeyEvent.VK_DOWN)
ball.move(0, 10);
return false;
}
});
}
}
对于BallComponent类：
static class BallComponent extends JComponent {
private double x = 225;
private double y = 225;
private Ellipse2D.Double ellipse = new Ellipse2D.Double(x, y, 50, 50);
public void move(int dX, int dY) {
x += dX;
y += dY;
ellipse = new Ellipse2D.Double(x, y, 50, 50);
repaint();
}
public void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.fill(ellipse);
}
}
答案 2 :(得分：2)
请看一下这段代码示例：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class PaintingPanel
{
private CustomPanel drawingArea;
private ActionMap actionMap;
private int x;
private int y;
private enum Direction
{
UP(KeyEvent.VK_UP),
DOWN(KeyEvent.VK_DOWN),
LEFT(KeyEvent.VK_LEFT),
RIGHT(KeyEvent.VK_RIGHT);
public int key;
private Direction(int key)
{
this.key = key;
}
public int getKey()
{
return key;
}
}
private class PanelAction extends AbstractAction
{
private Direction arrow;
public PanelAction(Direction a)
{
arrow = a;
}
@Override
public void actionPerformed(ActionEvent ae)
{
switch(arrow)
{
case UP:
y -= 1;
break;
case DOWN:
y += 1;
break;
case LEFT:
x -= 1;
break;
case RIGHT:
x += 1;
break;
}
drawingArea.setValues(x, y);
}
}
public PaintingPanel()
{
x = y = 5;
}
private void displayGUI()
{
JFrame frame = new JFrame("Painting Panel");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
drawingArea = new CustomPanel();
int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
InputMap inputMap = drawingArea.getInputMap(condition);
actionMap = drawingArea.getActionMap();
for (Direction arrow : Direction.values())
{
int key = arrow.getKey();
String name = arrow.name();
inputMap.put(KeyStroke.getKeyStroke(
key, 0), name);
actionMap.put(name, new PanelAction(arrow));
}
frame.setContentPane(drawingArea);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String... args)
{
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
new PaintingPanel().displayGUI();
}
});
}
}
class CustomPanel extends JPanel
{
private final int SIZE = 500;
private int x;
private int y;
private String text = "Hello World!";
public CustomPanel()
{
x = y = 5;
setOpaque(true);
setBackground(Color.WHITE);
}
public void setValues(int x, int y)
{
this.x = x;
this.y = y;
repaint();
}
@Override
public Dimension getPreferredSize()
{
return (new Dimension(SIZE, SIZE));
}
@Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
g.setColor(Color.GREEN.darker());
g.fillOval(x, y, 50, 50);
}
}