java - 在屏幕上移动球的情况下，如何正确处理 JComponent 的按键和重绘？

Question

我想我会尝试编写一个程序来绘制一个球，当按下箭头键时，将在屏幕上沿按下的方向移动球。首先，我开始尝试制作一个只执行“向上”箭头键动作的程序。

我四处寻找解决方案，但无法弄清楚这段代码有什么问题。我不知道这是否是我的输入和动作映射的问题（即程序识别按键的问题），或者是否是 JComponent 和 JFrame 类如何在摇摆中工作的问题。我想也许问题也可能是焦点；我真的不知道如何判断组件何时具有焦点。我认为现在该键已设置为 CNTRL+Y 而不是向上，只是因为在某些时候我认为我的字符串在输入地图制作器中指定向上箭头可能有问题。

在这一点上，我很沮丧，我只是想让这该死的东西做点什么，所以我使用的输入映射超出了必要的数量。

代码如下，它很短，格式很糟糕（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();
        }
    } 
}

score 2 · Accepted Answer

您似乎从未初始化actionPress- 尝试将其添加到您的 BallComponent 构造函数中：

actionPress = new ActionPress();

即，您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);
}

score 2 · Accepted Answer

您可以使用KeyboardFocusManager来监听箭头键的击键并更新球的位置。这是重新编写的代码：

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);
    }
}

score 2 · Accepted Answer

请看一下这个代码示例：

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);
    }
}

java - 在屏幕上移动球的情况下，如何正确处理 JComponent 的按键和重绘？

3 回答 3

Related

Reference