Java 如何在鼠标点击时调用 repaint()

Question

所以，我的代码基本上是这样的：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class Test extends JPanel{
    boolean circle = false;

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        this.setBackground(Color.WHITE);

        if(circle){
            g.drawRect(150,150,100,100);
        }
    }

    public static void main(String[] args){
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
        f.setSize(400,400);

        Test test = new Test();
        f.add(test);
    }
}

我希望当我单击鼠标时，circle 变量发生变化并调用 repaint()。

我该怎么做？谢谢

Answer 1

JPanel.addMouseListener就可以实现了。并注意 final 关键字在 jdk8 中是可选的，当内部 class.

中的变量访问时

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class Test extends JPanel {
    boolean circle = false;

    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        this.setBackground(Color.WHITE);

        if (circle) {
            g.drawRect(150, 150, 100, 100);
        }
    }

    public static void main(String[] args) {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
        f.setSize(400, 400);

        final Test test = new Test();
        test.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                test.circle = true;
                test.repaint();
            }
        });
        f.add(test);
    }
}

Answer 2

这是我曾经写过的一个小EventHandler...

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.*;
import java.awt.event.*;
import javax.swing.JFrame;
public class EventHandler implements KeyListener,MouseListener,MouseWheelListener {
    public JFrame pane;
    public int mouse_x;
    public int mouse_y;
    public int[] mouse=new int[5];
    public int[] keys=new int[256];
    @Override
     public void mousePressed(MouseEvent m) {
         //mouse[Math.abs(Math.min(3,m.getButton()-1))]=1;
         switch (m.getButton()) {
             case (MouseEvent.BUTTON1) :
                 mouse[2]=1;
             case (MouseEvent.BUTTON2) :
                 mouse[3]=1;
             case (MouseEvent.BUTTON3) :
                 mouse[4]=1;

         }
     }
     @Override
     public void mouseClicked(MouseEvent m) {
         //mouse[Math.abs(Math.min(3,m.getButton()-1))]=2;
         switch (m.getButton()) {
             case (MouseEvent.BUTTON1) :
                 mouse[2]=2;
             case (MouseEvent.BUTTON2) :
                 mouse[3]=2;
             case (MouseEvent.BUTTON3) :
                 mouse[4]=2;
         }
     }
     @Override
     public void mouseReleased(MouseEvent m) {
         //mouse[Math.abs(Math.min(3,m.getButton()-1))]=3;
         switch (m.getButton()) {
             case (MouseEvent.BUTTON1) :
                 mouse[2]=3;
             case (MouseEvent.BUTTON2) :
                 mouse[3]=3;
             case (MouseEvent.BUTTON3) :
                 mouse[4]=3;
         }
     }
     @Override
     public void mouseEntered(MouseEvent m) {
     }
     @Override
     public void mouseExited(MouseEvent m) {
     }
     @Override
     public void keyTyped(KeyEvent e) {
         keys[e.getKeyCode()]=2;
     }
     public void keyReleased(KeyEvent e) { 
         keys[e.getKeyCode()]=3;
     }
     public void keyPressed(KeyEvent e) {
         keys[e.getKeyCode()]=1;
     }
     public void updateKeys() {
         for (int i=0; i < keys.length; i++) {
             if (keys[i]==2 || keys[i]==3) {
                 keys[i]=0;
             }
         }
     }
     public void getMouse() {
         Component[] rel;
         rel = pane.getComponents();
         mouse_x=mouse[0]=MouseInfo.getPointerInfo().getLocation().x-rel[0].getLocationOnScreen().x;
         mouse_y=mouse[1]=MouseInfo.getPointerInfo().getLocation().y-rel[0].getLocationOnScreen().y;
     }
     public void updateMouse() {
         for (int i=0; i < mouse.length; i++) {
             if (mouse[i]==3 || mouse[i]==2)  {
                 mouse[i]=0;
             }
         }
     }
     public void mouseWheelMoved(MouseWheelEvent w) {
         mouse[3]=w.getWheelRotation();
     }
     public boolean isDown(int key) {
         if (keys[key]==1 || keys[key]==2) {
             return true;
         }
         else {
             return false;
         }
     }
     public void work() {
         getMouse();
     }
     public void reset() {
         updateKeys();
         updateMouse();
     }
    public EventHandler(JFrame plane) {
        this.pane=plane;
        pane.requestFocus();
        pane.addKeyListener(this);
        pane.addMouseListener(this);
    }
}

应用于您的代码：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

class Test extends JPanel{
    boolean circle = false;
    public EventHandler events; //EventHandler

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        this.setBackground(Color.WHITE);

        if(circle){
            g.drawRect(150,150,100,100);
        }
    }

    public static void main(String[] args){
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
        f.setSize(400,400);
        //
        events=new EventHandler(f);
        Test test = new Test();
        //f.add(test);
        f.setContentPane(test);
        while (true) {
            events.reset();
            events.work();
            dpane.repaint();
            if (events.mouse[2] != 0) {
                if (circle) {
                circle=false;
                }
                else {
                circle=true;
                }
            }
        }
    }
}

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