Java KeyBindings 在几秒钟后停止工作

Question

我正在尝试从 Java KeyListeners 转移到 KeyBindings 来进行动画处理，但它们会工作几秒钟，然后完全停止。当 Action 触发时，我将消息打印到控制台，并且这些消息停止，因此不仅仅是绘画不起作用，而是按下按键时触发了 Action 。

我的类扩展了 JFrame，我只是向它添加了一个 JPanel，并向 JPanel 添加了一个 JLabel。我使用由操作切换的标志来指示 JLabel 应如何移动，并使用 JFrame 的 actionPerformed 方法来检查标志的状态并调整 JLabel 的位置。

我尝试在 getInputMap 方法中添加 JComponent.WHEN_IN_FOCUSED_WINDOW，但没有什么区别。

代码如下:

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;

public class KeyBindingTest extends JFrame implements ActionListener {

    long counter = 0;
    int speed = 5;
    boolean isUp = false, isDown = false, isLeft = false, isRight = false;
    JLabel j = new JLabel();
    JPanel p = new JPanel();
    Timer t;

    Action upPressed = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("up on");
            isUp = true;
        }
    };
    Action upReleased = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            isUp = false;
            System.out.println("up off");
        }
    };
    Action downPressed = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("down on");
            isDown = true;
        }
    };
    Action downReleased = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("down off");
            isDown = false;
        }
    };
    Action leftPressed = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("left on");
            isLeft = true;
        }
    };
    Action leftReleased = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("left off");
            isLeft = false;
        }
    };
    Action rightPressed = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("right on");
            isRight = true;
        }
    };
    Action rightReleased = new AbstractAction() {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("right off");
            isRight = false;
        }
    };

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                // The try/catch block prevents errors from crashing the program
                try {
                    KeyBindingTest window = new KeyBindingTest(); // Create and setup the main game window
                    window.run(); // show the new window
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    private void run() {
        this.setBounds(640, 400, 640, 400);
        this.setVisible(true);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        p.setBounds(0, 0, this.getWidth(), this.getHeight());
        p.setVisible(true);
        p.setBackground(Color.blue);
        p.setOpaque(true);
        p.setFocusable(true);
        p.setLayout(null);
        j.setBounds(320, 200, 10, 10);
        j.setVisible(true);
        j.setBackground(Color.red);
        j.setOpaque(true);
        this.add(p);
        p.add(j);
        p.requestFocusInWindow();
        setupKeyBindings();
        t = new Timer(1000 / 40, this);
        t.start();
    }

    private void setupKeyBindings() {
        p.getInputMap().put(KeyStroke.getKeyStroke("W"), "moveUp");
        p.getActionMap().put("moveUp", upPressed);
        p.getInputMap().put(KeyStroke.getKeyStroke("released W"), "stopUp");
        p.getActionMap().put("stopUp", upReleased);
        p.getInputMap().put(KeyStroke.getKeyStroke("S"), "moveDown");
        p.getActionMap().put("moveDown", downPressed);
        p.getInputMap().put(KeyStroke.getKeyStroke("released S"), "stopDown");
        p.getActionMap().put("stopDown", downReleased);
        p.getInputMap().put(KeyStroke.getKeyStroke("A"), "moveLeft");
        p.getActionMap().put("moveLeft", leftPressed);
        p.getInputMap().put(KeyStroke.getKeyStroke("released A"), "stopLeft");
        p.getActionMap().put("stopLeft", leftReleased);
        p.getInputMap().put(KeyStroke.getKeyStroke("D"), "moveRight");
        p.getActionMap().put("moveRight", rightPressed);
        p.getInputMap().put(KeyStroke.getKeyStroke("released D"), "stopRight");
        p.getActionMap().put("stopRight", rightReleased);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        counter++;
        System.out.println(counter);
        if (isUp) {
            j.setLocation(j.getX(), j.getY() - speed);
        }
        if (isDown) {
            j.setLocation(j.getX(), j.getY() + speed);
        }
        if (isLeft) {
            j.setLocation(j.getX() - speed, j.getY());
        }
        if (isRight) {
            j.setLocation(j.getX() + speed, j.getY());
        }
        repaint();
    }

}

Answer 1

这是个人的事情，但是，如果您使用类似 KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false) 的方法，通常会遇到更少的问题KeyStroke.getKeyStroke("W")

KeyStroke.getKeyStroke("released W") 的等效项是 KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true)我已经反复浏览了您的示例，我尝试将 KeyStroke.getKeyStroke("W") 替换为 KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false) 及其等效项；我尝试用 Set 替换 boolean 标志，但仍然遇到同样的问题

然后我扔掉了你的代码并开始了一个新项目。首先我尝试了自定义绘画路线，效果很好。然后我尝试了基于组件的路线并且有效......😓

所以，虽然我仍然没有一个“答案”来解释为什么它不起作用，但我确实有一个例子......

示例

因为我实际上已经测试了我的建议......

import com.sun.glass.events.KeyEvent;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.HashSet;
import java.util.Set;
import javax.swing.AbstractAction;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
import javax.swing.Timer;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        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 TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public enum Input {
        UP, DOWN, LEFT, RIGHT
    }

    public class TestPane extends JPanel {

        private Set<Input> inputs = new HashSet<>();

        private int delta = 4;

        private JLabel label;

        public TestPane() {
            InputMap inputMap = getInputMap(WHEN_IN_FOCUSED_WINDOW);
            ActionMap actionMap = getActionMap();

            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, false), "Up.pressed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0, true), "Up.relesed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, false), "Down.pressed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_S, 0, true), "Down.relesed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, false), "Left.pressed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_A, 0, true), "Left.relesed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, false), "Right.pressed");
            inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_D, 0, true), "Right.relesed");

            actionMap.put("Up.pressed", new InputAction(Input.UP, true));
            actionMap.put("Up.relesed", new InputAction(Input.UP, false));
            actionMap.put("Down.pressed", new InputAction(Input.DOWN, true));
            actionMap.put("Down.relesed", new InputAction(Input.DOWN, false));
            actionMap.put("Left.pressed", new InputAction(Input.LEFT, true));
            actionMap.put("Left.relesed", new InputAction(Input.LEFT, false));
            actionMap.put("Right.pressed", new InputAction(Input.RIGHT, true));
            actionMap.put("Right.relesed", new InputAction(Input.RIGHT, false));

            setLayout(null);
            label = new JLabel();
            label.setBackground(Color.RED);
            label.setOpaque(true);
            label.setBounds(0, 0, 10, 10);
            add(label);

            Timer timer = new Timer(5, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    int xPos = label.getX();
                    int yPos = label.getY();
                    if (inputs.contains(Input.UP)) {
                        yPos -= delta;
                    }
                    if (inputs.contains(Input.DOWN)) {
                        yPos += delta;
                    }
                    if (inputs.contains(Input.LEFT)) {
                        xPos -= delta;
                    }
                    if (inputs.contains(Input.RIGHT)) {
                        xPos += delta;
                    }

                    if (xPos < 0) {
                        xPos = 0;
                    } else if (xPos + 10 > getWidth()) {
                        xPos = getWidth() - 10;
                    }
                    if (yPos < 0) {
                        yPos = 0;
                    } else if (yPos + 10 > getHeight()) {
                        yPos = getHeight() - 10;
                    }
                    label.setLocation(xPos, yPos);
                    repaint();
                }
            });
            timer.start();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

//        protected void paintComponent(Graphics g) {
//            super.paintComponent(g);
//            Graphics2D g2d = (Graphics2D) g.create();
//            g2d.setColor(Color.RED);
//            g2d.drawRect(xPos, yPos, 10, 10);
//            g2d.dispose();
//        }

        public class InputAction extends AbstractAction {
            private Input input;
            private boolean pressed;

            public InputAction(Input input, boolean pressed) {
                this.input = input;
                this.pressed = pressed;
            }

            @Override
            public void actionPerformed(ActionEvent e) {
                if (pressed) {
                    inputs.add(input);
                } else {
                    inputs.remove(input);
                }
            }
        }
    }

}

旁注...

这种“类型”的问题最近被问到很多，我认为这是某种类作业，因为我们已经看到了这种代码风格的许多变体。正如我们一再建议的那样，以这种方式使用组件是不明智的，它们并不是真正为这种事情而设计的。使用自定义绘画路线，您将获得更好(且更容易)的结果，如 Make an JLabel move with Key Bidings 中所示。