鼠標監聽器不能使用JPanel

Question

paintcomponent工作正常，圖像顯示出來，沒有問題，或者與JFrame。我想實現縮放和平移，但沒有得到任何運氣，因爲添加的鼠標監聽器沒有響應。

import java.awt.Graphics; 
import java.awt.event.MouseEvent; 
import java.awt.event.MouseListener; 
import java.awt.event.MouseAdapter; 
import javax.swing.JPanel; 
import java.awt.image.BufferedImage; 
import java.io.File; 
import java.io.IOException; 
import java.util.logging.Level; 
import java.util.logging.Logger; 
import javax.imageio.ImageIO; 

public class map extends JPanel { 
    public int moz = 100; 
    public void map() 
    { 
     addMouseListener(
       new MouseAdapter() 
       { 
        @Override 
        public void mouseClicked(MouseEvent e) 
        { 
         moz = moz +100; 
         repaint(); 
        } 
       } 
     ); 
    } 
    public void paintComponent(Graphics g){ 
     ..... 
     g.drawLine(0, moz, 100, 0); 
    } 
} 

Answer 1

你的類沒有一個真正的構造，而是有一個「僞」的構造函數，因爲它有一個返回類型 - 是void計數。因此，通過改變擺脫void返回類型：

// this is not a constructor 
public void map() 

到：

// this is a real constructor 
public map() 

另外，作爲一個側面建議，改變你的變量和類名與Java命名約定相一致：類名全部啓動用大寫字母和方法/變量名稱以小寫字母表示。

所以你的情況你命名你的類地圖，並與代碼打能有這樣的：

import java.awt.BasicStroke; 
import java.awt.Color; 
import java.awt.Dimension; 
import java.awt.Graphics; 
import java.awt.Graphics2D; 
import java.awt.Point; 
import java.awt.Rectangle; 
import java.awt.Stroke; 
import java.awt.event.MouseAdapter; 
import java.awt.event.MouseEvent; 
import java.awt.image.BufferedImage; 
import java.util.ArrayList; 
import java.util.List; 
import java.util.Random; 

import javax.swing.*; 

public class Map extends JPanel { 
    private static final int PREF_W = 800; 
    private static final int PREF_H = 650; 
    private static final Color DRAW_RECT_COLOR = new Color(200, 200, 255); 
    public static final Stroke IMAGE_STROKE = new BasicStroke(3f); 
    public static final Color IMAGE_COLOR = Color.RED; 
    private BufferedImage image = new BufferedImage(PREF_W, PREF_H, BufferedImage.TYPE_INT_ARGB); 
    private Rectangle drawRectangle = null; 
    private List<Color> colors = new ArrayList<>(); 
    private Random random = new Random(); 

    public Map() { 
     MyMouse myMouse = new MyMouse(); 
     addMouseListener(myMouse); 
     addMouseMotionListener(myMouse); 
     for (int r = 0; r < 4; r++) { 
      int r1 = (r * 255)/3; 
      for (int g = 0; g < 4; g++) { 
       int g1 = (g * 255)/3; 
       for (int b = 0; b < 4; b++) { 
        int b1 = (b * 255)/3; 
        colors.add(new Color(r1, g1, b1)); 
       } 
      } 
     } 
    } 

    @Override 
    protected void paintComponent(Graphics g) { 
     super.paintComponent(g); 
     g.drawImage(image, 0, 0, this); 
     Graphics2D g2 = (Graphics2D) g; 
     if (drawRectangle != null) { 
      g.setColor(DRAW_RECT_COLOR); 
      g2.draw(drawRectangle); 
     } 
    } 

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

    private class MyMouse extends MouseAdapter { 
     Point p1 = null; 

     @Override 
     public void mousePressed(MouseEvent e) { 
      p1 = e.getPoint(); 
     } 

     @Override 
     public void mouseDragged(MouseEvent e) { 
      if (p1 == null) { 
       return; 
      } 
      Point p2 = e.getPoint(); 
      drawRectangle = createDrawRect(p2); 
      repaint(); 
     } 

     @Override 
     public void mouseReleased(MouseEvent e) { 
      Rectangle rectangle = createDrawRect(e.getPoint()); 
      Graphics2D g2 = image.createGraphics(); 
      g2.setStroke(IMAGE_STROKE); 
      Color c = colors.get(random.nextInt(colors.size())); 
      g2.setColor(c); 
      g2.draw(rectangle); 
      g2.dispose(); 
      p1 = null; 
      drawRectangle = null; 
      repaint(); 
     } 

     private Rectangle createDrawRect(Point p2) { 
      int x = Math.min(p1.x, p2.x); 
      int y = Math.min(p1.y, p2.y); 
      int w = Math.abs(p1.x - p2.x); 
      int h = Math.abs(p1.y - p2.y); 
      return new Rectangle(x, y, w, h); 
     } 

    } 

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

     JFrame frame = new JFrame("Map"); 
     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(); 
      } 
     }); 
    } 
}