我想我会尝试写一个程序，能画出一个球，而且当按下方向键，将移动球在屏幕上压入的方向。 首先我开始尝试做一个计划，该计划只是做“UP”箭头键移动。
我看了看周围的解决方案，只是无法弄清楚什么是错与此代码。 我不知道这是否是我的输入和行动的地图有问题（即与程序识别的按键有问题），或者如果它与的JComponent和JFrame的类中摇摆如何工作的问题。 我想，也许这个问题也可能是重点; 我真的不知道如何告诉当一个组件具有焦点。 我认为，关键已被设置为CNTRL + Y代替了现在，只是因为在某些时候我想这可能是我的字符串输入地图制造商指定的向上箭头的问题。
在这一点上，我很沮丧，我只是试图让该死的东西做一些事情 ，所以我使用超过输入的地图应该是必要的。
代码如下所示，这是很短，格式化可怕的（不好意思）：
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();
}
}
}
看来你从来没有初始化actionPress -尝试添加这对您的BallComponent构造函数：
actionPress = new ActionPress();
也就是说，你的构造是这样的
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);
}
您可以使用KeyboardFocusManager监听箭头键的按键和更新球的位置。 下面是重新设计的代码：
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;
}
});
}
}
而对于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);
}
}
请你看看这个代码示例：
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);
}
}
文章来源: How does one properly handle keypresses and repainting of a JComponent in the context of moving a ball around a screen?
