java - 键盘不输入任何东西java

Question

我一直在尝试这段代码并对其进行编辑，但它不起作用。假设得到一个键盘输入，将其存储在变量“c”中，然后进行比较到键盘上的键。然后假设根据按下的键移动一个小方 block 。键盘似乎无法识别。有人可以帮帮我吗？请注意我 14 岁，所以请不要说它是多么简单和容易，我还在学习，你能不能也用我可能理解的方式来写它。提前谢谢你

'package package1;

import java.awt.Color;
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.JFrame;
import javax.swing.JPanel;
import javax.swing.Timer;

public class Class1 extends JPanel implements KeyListener, ActionListener{

Timer timer = new Timer(5, this);

//variables    
int cox = 0;
int spx = 0;  //cox = coordinates x, spx = speedx
int coy = 0;
int spy = 0;  //coy = coordinates y, spy = speedy

public void paintComponent(Graphics g)
{
    timer.start();

    super.paintComponent(g);
    g.setColor(Color.BLUE);     
    g.fillRect(cox, coy, 50, 50);

    addKeyListener(this);
    setFocusable(true);
    setFocusTraversalKeysEnabled(false);
}

public void actionPerformed(ActionEvent e)
{
    cox = cox + spx;
    coy = coy + spy;
    repaint();
}

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

    if(c == KeyEvent.VK_LEFT)
    {
        spx = -1;
        spy = 0;
    }
    if(c == KeyEvent.VK_UP)
    {
        spx = 0;
        spy = -1;
    }
    if(c == KeyEvent.VK_RIGHT)
    {
        spx = 1;
        spy = 0;
    }
    if(c == KeyEvent.VK_DOWN)
    {
        spx = 0;
        spy = 1;
    }

}

public void keyTyped(KeyEvent e)
{
}
public void keyReleased(KeyEvent e)
{
    spx = 0;
    spy = 0;
}

public static void main(String args[])
{
    Class1 t = new Class1();
    JFrame frame = new JFrame("window");
    frame.setSize(500,500);
    frame.setVisible(true);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(t);
}
}

Answer 1

你的代码有问题:

• KeyListener 是非常低级的构造，通常应避免使用 大多数 Swing 应用程序中的键绑定(bind)。这样做还可以更轻松地解决困扰 KeyListener 的焦点问题，这些问题会导致您当前的 KeyListener 什么都不做。如果您在这个站点上阅读了大多数带有 Swing 和 KeyListeners 标签的问题，您会一次又一次地看到这个建议——因为它是真实的，而且有效。
• 请理解 paintComponent(Graphics g) 方法仅用于绘制。它经常被调用，通常不受您的控制，因为操作系统可以诱导它被调用。
• paintComponent 方法对 GUI 的感知响应能力有重大影响，因为它控制绘制 GUI 和 GUI 可能包含的任何动画。如果它因任何原因而变慢，您的 GUI 将看起来很慢。
• 出于这个原因，此方法应该用于绘图，并且只用于绘图，仅绘图。具体来说，
  • 不要从此方法中启动您的 Swing 计时器，
  • 不要从此方法中添加 KeyListener(除非您想向 GUI 添加 KeyListener 20 次，这将导致极其不可预测的行为)，
  • 不要在此方法中更改任何对象的状态。

---

例如:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

import javax.swing.*;

@SuppressWarnings("serial")
public class Class1B extends JPanel {   
   private static final int PREF_W = 500;
   private static final int PREF_H = PREF_W;
   private static final int ANIMATION_DELAY = 15;
   private static final int RECT_WIDTH = 15;
   private static final Color RECT_COLOR = Color.red;
   private EnumMap<Direction, Boolean> dirMap = new EnumMap<>(Direction.class);
   private Map<Integer, Direction> keyToDir = new HashMap<>();
   private Timer animationTimer;
   public int rectX;
   public int rectY;


   public Class1B() {
      for (Direction dir : Direction.values()) {
         dirMap.put(dir, Boolean.FALSE);
      }
      keyToDir.put(KeyEvent.VK_UP, Direction.UP);
      keyToDir.put(KeyEvent.VK_DOWN, Direction.DOWN);
      keyToDir.put(KeyEvent.VK_LEFT, Direction.LEFT);
      keyToDir.put(KeyEvent.VK_RIGHT, Direction.RIGHT);
      setKeyBindings();

      animationTimer = new Timer(ANIMATION_DELAY, new AnimationListener());
      animationTimer.start();
   }

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

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      g.setColor(RECT_COLOR);
      g.fillRect(rectX, rectY, RECT_WIDTH, RECT_WIDTH);
   }

   private void setKeyBindings() {
      int condition = WHEN_IN_FOCUSED_WINDOW;
      final InputMap inputMap = getInputMap(condition);
      final ActionMap actionMap = getActionMap();
      boolean[] keyPressed = { true, false };
      for (Integer keyCode : keyToDir.keySet()) {
         Direction dir = keyToDir.get(keyCode);
         for (boolean onKeyPress : keyPressed) {
            boolean onKeyRelease = !onKeyPress;
            KeyStroke keyStroke = KeyStroke.getKeyStroke(keyCode, 0,
                  onKeyRelease);
            Object key = keyStroke.toString();
            inputMap.put(keyStroke, key);
            actionMap.put(key, new KeyBindingsAction(dir, onKeyPress));
         }
      }
   }

   private class KeyBindingsAction extends AbstractAction {
      private Direction dir;
      boolean pressed;

      public KeyBindingsAction(Direction dir, boolean pressed) {
         this.dir = dir;
         this.pressed = pressed;
      }

      @Override
      public void actionPerformed(ActionEvent evt) {
         dirMap.put(dir, pressed);
      }
   }

   private class AnimationListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent evt) {
         boolean repaint = false;
         for (Direction dir : Direction.values()) {
            if (dirMap.get(dir)) {
               rectX += dir.getIncrX();
               rectY += dir.getIncrY();
               repaint = true;
            }
         }
         if (repaint) {
            repaint();
         }
      }
   }

   private static void createAndShowGui() {
      Class1B mainPanel = new Class1B();

      JFrame frame = new JFrame("Class1B");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

enum Direction {
   UP(0, -1), DOWN(0, 1), LEFT(-1, 0), RIGHT(1, 0);
   private int incrX;
   private int incrY;

   private Direction(int incrX, int incrY) {
      this.incrX = incrX;
      this.incrY = incrY;
   }

   public int getIncrX() {
      return incrX;
   }

   public int getIncrY() {
      return incrY;
   }
}