如何在每个并发线程中在 Java Swing 中绘画？

Question

我的程序的目标是从随机生成的点中绘制正方形。 我想在每个线程生成一组方块后立即显示它们。 但是，一旦所有线程都运行完毕，只会显示一组方块。 我使用过swinginvoke，并且很好奇，好像repaint() 有问题，因为所有线程都达到了重绘但在最后一个线程完成之前不会绘制，并最终相互重叠。 我也不希望在每个线程之间共享“storedata”变量，但它的每个实例都将数据保存在其中。 我试图通过清除它来解决这个问题，但它没有奏效。 该程序由自定义线程类、线程启动的主类、GUI 类和绘制正方形的自定义 jpanel 组成。

import java.awt.*;
import java.util.Random;
import java.util.concurrent.CopyOnWriteArrayList;

class Action extends Thread {

        private Random rand = new Random();
        private static CopyOnWriteArrayList<Point> storedata = new CopyOnWriteArrayList<>();
        static volatile CopyOnWriteArrayList<CopyOnWriteArrayList<Point>> finallist = new CopyOnWriteArrayList<>();
        private GUI g;

        Action(GUI g) {
            this.g = g;

        }

    private void generatePoint() {
        int x = rand.nextInt(500);
        int y = rand.nextInt(500);
        Point p = new Point(x,y);
        storedata.add(p);

    }

    public void run() {
        for (int i = 0; i < 5; i++) {
            generatePoint();
        }
        CopyOnWriteArrayList<Point> copy = new CopyOnWriteArrayList<>(storedata);
        finallist.add(copy);
        SwingUtilities.invokeLater(() -> {
            try {
                Thread.sleep(500);
                System.out.println("ARRAY = " + copy.toString());
                g.setSolution(copy);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        storedata.clear();
    }
}

public class Main {
    public static void main(String[] args) {
        GUI g = new GUI();
        g.setVisible(true);

        Thread[] threads = new Thread[5];
        for (int i = 0; i < threads.length; i++) {
            threads[i] = new Action(g);
            threads[i].start();
        }

    }


import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.CopyOnWriteArrayList;

public class GUI extends JFrame implements ActionListener  {
    private CustomPanel c;
    GUI()  {
        initialize();
    }


    private void initialize()  {
        this.setLayout(new FlowLayout());
        c = new CustomPanel(500,500);
        this.setSize(1000,1000);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.add(c);
        this.setTitle("Seat Placement Program");
    }

    @Override
    public void actionPerformed(ActionEvent e) {

    }

    public void setSolution(CopyOnWriteArrayList<Point> room) {
        c.setRoom(room);
        c.setPaint(true);
        c.repaint();
    }

import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.CopyOnWriteArrayList;

public class CustomPanel extends JPanel implements ActionListener {

    private Border blackline = BorderFactory.createLineBorder(Color.black);
    private boolean paint;
    private CopyOnWriteArrayList<Point> room;

    public CustomPanel(int h, int w) {
        room = new CopyOnWriteArrayList<>();
        paint = false;
        this.setPreferredSize(new Dimension(w,h));
        this.setBorder(blackline);
    }

    @Override
    public void actionPerformed (ActionEvent e) {

    }


    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        if(paint) {
            for(Point p : room) {
                g.drawRect((int) p.getX(),(int) p.getY(),20,20);
            }
        }
    }

    void setPaint(boolean b) {
        paint = b;
    }

    public void setRoom(CopyOnWriteArrayList<Point> room) {
        this.room = room;
    }


}

Answer 1

在 Swing 中，绘制只能在Event Dispatching Thread 中完成。 实现您想要的方法是当线程完成时，将形状（可能连同颜色）添加到您想要它的 JComponent 集合中（您需要创建一个具有此类集合的自定义 JComponent，并且您应该在添加形状时和在绘制形状时在paintComponent 中同步它）。 然后在您的非 EDT 线程中，调用 myJComponent.repaint()。 可以在所有非 EDT 线程中调用它。

例子：

public class MyPanel extends JPanel {
  Collection<Shape> myShapes = ...;
  public void paintComponent(Graphics g) {
    ... // do any other non-shape related painting
    Graphics2D g2 = (Graphics2D) g;
    synchronized (myShapes) {
      for (Shape s : myShapes) {
        //TODO: do you want to set a color?
        g.draw(s);
        //TODO: do you want to fill the shapes?
        g.fill(s);
      }
    }
  }
}

然后在你的线程中：

public void run() {
  ...
  Shape newShape = ...;
  synchronized (myPanel.myShapes) {
    //add newShape to the collection
  }
  myPanel.repaint();
}