为 keylistener 请求焦点，不确定我是否有焦点？

Question

我不知道为什么当我按下 w 时，我的矩形没有相应地调整。我的重点设置是否正确，还是需要从单独的班级申请？我应该在我的drawingComponent 班级还是在我的“核心”班级中这样做？

package scratch;


import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.util.*;

public class drawingComponent extends JComponent implements KeyListener {

    Rectangle hello = new Rectangle(300, 100, 50, 50);

    public void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D) g;
        g2.setColor(new Color(255,25,0));
        g2.setFont(new Font("monospace", Font.BOLD+Font.ITALIC, 30));
        g2.drawString("nothing yet",300,320);
        g2.fill(hello);

    }


    @Override
    public void keyPressed(KeyEvent e) {

        if(e.getKeyCode() == KeyEvent.VK_W){

             hello.setLocation(hello.x-50, hello.y);
             repaint();

        }


    }

    @Override
    public void keyReleased(KeyEvent e) {


    }

    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub

    }

}

我通过将以下内容添加到我的 drawingComponent 类中解决了这个问题。

setFocusable(true);
requestFocus();
addKeyListener(this);

Answer 1

您想使用Key Bindings，而不是 KeyListener 有几个原因，但其中一个原因是您不必太担心 Key Bindings 的焦点。此外，您将来会希望发布一个minimal example program，我们可以测试、运行和修改，如下所示：

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.*;

public class DrawingComponent extends JPanel {
   private static final int PREF_W = 800;
   private static final int PREF_H = 600;
   private static final Color RECT_COLOR = new Color(255,25,0);
   private Rectangle rect = new Rectangle(300, 100, 50, 50);

   public DrawingComponent() {
      setUpKeyBindings();
   }

   private void setUpKeyBindings() {
      int condition = WHEN_IN_FOCUSED_WINDOW;
      InputMap inputMap = getInputMap(condition);
      ActionMap actionMap = getActionMap();

      KeyStroke wStroke = KeyStroke.getKeyStroke(KeyEvent.VK_W, 0);
      inputMap.put(wStroke, wStroke.toString());
      actionMap.put(wStroke.toString(), new WAction());
   }

   @Override
   protected void paintComponent(Graphics g) {
      super.paintComponent(g);
      Graphics2D g2 = (Graphics2D) g;
      g2.setColor(RECT_COLOR);
      g2.fill(rect);
   }

   @Override
   public Dimension getPreferredSize() {
      if (isPreferredSizeSet()) {
         return super.getPreferredSize();
      }
      return new Dimension(PREF_W, PREF_H);
   }

   private class WAction extends AbstractAction {
      @Override
      public void actionPerformed(ActionEvent e) {
         rect.setLocation(rect.x-50, rect.y);
         repaint();
      }
   }

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

      JFrame frame = new JFrame("DrawingComponent");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_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();
         }
      });
   }
}

另外，在你的覆盖中调用 super 的 paintComponent 方法，否则你的 JPanel 不会删除旧图像。