java - Dr java keylistener 帮助对象在按键释放后移动

Question

我正在尝试创建一个程序，其中一个对象会不断地从屏幕上掉下来，除非用户按下空格键，在这种情况下它会向上移动。到目前为止，当我运行程序时，我已经让物体开始下落。当我按下空格键时，对象会向上移动(就像它应该的那样)。但是，当我松开按键时，物体停止移动。我希望松开 key 时它继续下降。

我考虑过使用按键绑定(bind)而不是按键监听器，但我遇到了麻烦。我是一名高中生，希望主修计算机科学，所以请原谅我不了解太多高级编码术语/方法。然而，我是类最好的学生之一，也是一个渴望解决这个问题的快速学习者。这是我的代码:

public class htestnew extends JPanel implements ActionListener, KeyListener {
    Timer t = new Timer(5, this);
    int x = 20, y = 20, vely = 1;

    public htestnew() {
        t.start();
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        ImageIcon background = new ImageIcon("OBJECTEXAMPLE1");
        background.paintIcon(this, g, 0, 0);
    }

    public void actionPerformed(ActionEvent e) {
        if (y < 0)
        {
            vely = 0;
            y = 0;
        }

        if (y > 305) //-70
        {
            vely = 0;
            y = 305;
        }

        y += vely;
        repaint();
    }

    public void keyPressed(KeyEvent e) {
        int code = e.getKeyCode();

        if (code == KeyEvent.VK_SPACE) {
            vely = -1;
        }
    }

    public void keyTyped(KeyEvent e) {
    }

    public void keyReleased(KeyEvent e) {
        vely = 0;
        //I have tried setting this value to 1 but it does not work
    }

如果使用键绑定(bind)更容易，那么个人且易于遵循的示例将是令人惊奇的。谢谢。

Answer 1

所以，改变...

public void keyReleased(KeyEvent e) {
 vely=0;
//I have tried setting this value to 1 but it does not work
}

到...

public void keyReleased(KeyEvent e) {
 vely=1;
//I have tried setting this value to 1 but it does not work
}

基本上让它工作了(在我添加了一些实际绘制的东西之后)

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test extends JPanel implements ActionListener, KeyListener {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new Test());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    Timer t = new Timer(5, this);
    int x = 20, y = 20, vely = 1;

    public Test() {
        t.start();
        addKeyListener(this);
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 300);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(x, y, 5, 5);
    }

    public void actionPerformed(ActionEvent e) {

        if (y < 0) {
            vely = 0;
            y = 0;
        }

        if (y > 305) //-70
        {
            vely = 0;
            y = 305;
        }

        y += vely;
        repaint();
    }

    public void keyPressed(KeyEvent e) {
        int code = e.getKeyCode();

        if (code == KeyEvent.VK_SPACE) {
            vely = -1;
        }

    }

    public void keyTyped(KeyEvent e) {
    }

    public void keyReleased(KeyEvent e) {
        vely = 1;
//I have tried setting this value to 1 but it does not work
    }
}

我强烈建议您查看How to Use Key Bindings而不是使用KeyListener，它将用KeyListener解决核心问题

按键绑定(bind)示例...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.AbstractAction;
import javax.swing.Action;
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 Test extends JPanel implements ActionListener {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new Test());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    Timer t = new Timer(5, this);
    int x = 20, y = 20, vely = 1;

    public Test() {
        t.start();

        addKeyBinding("space.pressed", KeyEvent.VK_SPACE, true, new ChangeYAction(-1));
        addKeyBinding("space.released", KeyEvent.VK_SPACE, false, new ChangeYAction(1));
    }

    protected void addKeyBinding(String name, int virtualKey, boolean pressed, Action action) {
        addKeyBinding(name, KeyStroke.getKeyStroke(virtualKey, 0, !pressed), action);
    }

    protected void addKeyBinding(String name, KeyStroke keyStroke, Action action) {
        InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
        ActionMap am = getActionMap();

        im.put(keyStroke, name);
        am.put(name, action);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(300, 300);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawRect(x, y, 5, 5);
    }

    public void actionPerformed(ActionEvent e) {

        if (y < 0) {
            vely = 0;
            y = 0;
        }

        if (y > 305) //-70
        {
            vely = 0;
            y = 305;
        }

        y += vely;
        repaint();
    }

    public class ChangeYAction extends AbstractAction {

        private int changeYTo;

        public ChangeYAction(int changeYTo) {
            this.changeYTo = changeYTo;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            vely = changeYTo;
        }

    }

}