如何消除keyPress的延迟？

Question

因此，我已经看到了一些与此相关的主题，并且需要一些有关如何专门修复它的帮助。按住某个键时，Java将读取第一次按键，然后稍有延迟，然后它将连续读取按键，直到您松开按键为止。

public void keyPressed(KeyEvent key) {
    int code = key.getKeyCode();
    if (code == KeyEvent.VK_DOWN) {
        //Do stuff
    }
    if (code == KeyEvent.VK_LEFT) {
        //Do stuff
    }
    if (code == KeyEvent.VK_RIGHT) {
        //Do stuff
    }
    if (code == KeyEvent.VK_UP) {
        //Do stuff
    }
}

那是我当前的代码。我听说要解决此问题，您可以创建一个计时器来快速检查按键是否按下，但是我不确定如何执行此操作。在这里或者如果有更好的解决方案，将不胜感激。

Answer 1

您问题的基本答案是，延迟不能是特定于操作系统的。

更长的答案是，您应该忽略各个事件本身，并通过使用适当的标志监视状态变化（在按下和释放之间）。

这意味着，当按下某个键时，您将设置一些标志，程序可以使用该标志来更改程序的状态，并在释放标志时将其重置。

这使事件与状态更改脱离关联，并为您提供了更大的灵活性，因为您的程序不在乎是什么原因导致状态更改，而只是在乎状态已更改并且应该对此做出反应。

这将需要您承担某种“循环”，其职责是监视此更改并做出相应的反应。在游戏中，这通常称为“游戏循环”，但也可以称为“主循环”。

正是这种“循环”责任来更新程序的状态并对其进行绘制。

下面是一个非常简单的示例，该示例使用键绑定API和javax.swing.Timer演示了基本概念

import com.sun.glass.events.KeyEvent;
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.AbstractAction;
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 MoveMe {

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

    public MoveMe() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

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

    public class MovementState {

        public int xDirection;
        public int yDirection;

    }

    public class TestPane extends JPanel {

        private MovementState movementState;
        private Rectangle box;

        public TestPane() {
            movementState = new MovementState();
            InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
            ActionMap am = getActionMap();

            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, false), "down-pressed");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0, true), "down-released");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, false), "up-pressed");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0, true), "up-released");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, false), "left-pressed");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0, true), "left-released");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, false), "right-pressed");
            im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0, true), "right-released");

            am.put("down-pressed", new YDirectionAction(movementState, 2));
            am.put("down-released", new YDirectionAction(movementState, 0));
            am.put("up-pressed", new YDirectionAction(movementState, -2));
            am.put("up-released", new YDirectionAction(movementState, 0));
            am.put("left-pressed", new XDirectionAction(movementState, -2));
            am.put("left-released", new XDirectionAction(movementState, 0));
            am.put("right-pressed", new XDirectionAction(movementState, 2));
            am.put("right-released", new XDirectionAction(movementState, 0));

            box = new Rectangle(90, 90, 20, 20);

            Timer timer = new Timer(40, new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    box.x += movementState.xDirection;
                    box.y += movementState.yDirection;
                    if (box.x < 0) {
                        box.x = 0;
                    } else if (box.x + box.width > getWidth()) {
                        box.x = getWidth() - box.width;
                    }
                    if (box.y < 0) {
                        box.y = 0;
                    } else if (box.y + box.height > getHeight()) {
                        box.y = getHeight() - box.height;
                    }
                    repaint();
                }
            });
            timer.start();
        }

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

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(Color.RED);
            g2d.fill(box);
            g2d.dispose();
        }
    }

    public abstract class AbstractDirectionAction extends AbstractAction {

        private final MovementState movementState;
        private final int value;

        public AbstractDirectionAction(MovementState movementState, int value) {
            this.movementState = movementState;
            this.value = value;
        }

        public MovementState getMovementState() {
            return movementState;
        }

        public int getValue() {
            return value;
        }

    }

    public class YDirectionAction extends AbstractDirectionAction {

        public YDirectionAction(MovementState movementState, int value) {
            super(movementState, value);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            getMovementState().yDirection = getValue();
        }

    }

    public class XDirectionAction extends AbstractDirectionAction {

        public XDirectionAction(MovementState movementState, int value) {
            super(movementState, value);
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            getMovementState().xDirection = getValue();
        }

    }

}