java - 如何制作不会更新的 JPanel 背景？

Question

我正在尝试制作一个动画屏幕保护程序，其中包含一些不断变化的颜色和移动的形状，并且我还希望它具有某种轨迹效果(例如，如果您不这样做，每个像素上的最新颜色将不断绘制在那里)设置背景颜色)。我以前实现过一次这种效果，但不知道是怎么做到的。目前的结果是一个移动的方 block ，它可以在灰色背景上改变颜色。屏幕保护程序.java

import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JPanel;
import javax.swing.Timer;

public class ScreenSaver extends JPanel
{
    public static Component sc;
    public int delay = 1000/2;
    public int state = 0;
    public int re = 255;
    public int gr = 0;
    public int bl = 0;
    public int d = 1;
    ScreenSaver()
    {
        ActionListener counter = new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                updateUI();
                repaint();
            }
        };
        new Timer(delay, counter).start();
        System.out.println("this is the secret screensaver that appears after 30 seconds of no mouse activity");//i have this line here so it doesn't print every time the screen updates
    }

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        this.setBackground(null);
        if (state == 0)
        {
            gr++;
            if(gr == 255)
                state = 1;
        }
        if (state == 1)
        {
            re--;
            if(re == 0)
                state = 2;
        }
        if (state == 2)
        {
            bl++;
            if(bl == 255)
                state = 3;
        }
        if (state == 3)
        {
            gr--;
            if(gr == 0)
                state = 4;
        }
        if (state == 4)
        {
            re++;
            if(re == 255)
                state = 5;
        }
        if (state == 5)
        {
            bl--;
            if(bl == 0)
                state = 0;
        }
        g.setColor(new Color(re, gr, bl));
        d++;
        g.fillRect(d, 50, 50, 50);
    }
    public static void main(String[] args)
    {
        //ScreenSaver sc = new ScreenSaver();
    }
}

Main.java:(通过该文件将ScreenSaver.java作为对象调用)

import java.awt.Color;
import java.awt.Graphics;
//import java.util.Random;

//import javax.swing.AbstractAction;
//import javax.swing.Action;
import javax.swing.JFrame;
import javax.swing.JPanel;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;

import javax.swing.Timer;

public class FinalProject extends JPanel implements MouseMotionListener
{
    public int delay = 1000/2;
    public boolean screenActive = true;
    public int why = 1;
    FinalProject()
    {
        ActionListener counter = new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                updateUI();
                repaint();
            }
        };
        new Timer(delay, counter).start();
    }
    static JFrame jf = new JFrame();

    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        this.setBackground(Color.BLACK);
        if (screenActive)
        {
            why++;
        }
        if (why == 6)
        {
            why = 0;
            System.out.println("inactivity detected");
            screenActive = false;
            ScreenSaver sc = new ScreenSaver();
            jf.add(sc);
        }
    }

    public static void main(String[] args) throws InterruptedException
    {
        System.out.println("Welcome to Computer Simulator 0.1");
        System.out.println("this is the main screen");
        FinalProject e = new FinalProject();
        //ScreenSaver sc = new ScreenSaver();
        jf.setTitle("game");
        jf.setSize(500,500);
        //jf.setUndecorated(true);
        //jf.setBackground(new Color(1.0f,1.0f,1.0f,0.5f));
        jf.setVisible(true);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //jf.add(new ScreenSaver());
        jf.add(e);
    }

    @Override
    public void mouseDragged(MouseEvent arg0) {
        // TODO Auto-generated method stub

    }

    @Override
    public void mouseMoved(MouseEvent MOUSE_MOVED)
    {

    }
}

Answer 1

不要调用 updateUI()。您所需要的只是 repaint() 来使组件重新绘制自身。

一种方法是对 BufferedImage 进行绘图，然后使用 BufferedImage 创建一个 ImageIcon，并将其添加到 JLabel 中。

另一种方法是保留要绘制的对象的列表，然后在每次重新绘制组件时迭代该列表。

查看Custom Painting Approches了解工作示例以及何时可以使用这两种方法的分析。