JComponent.paintImmediately()如何在Java Swing中运行？

我的理解：
与JComponent.repaint()中Swing调用的大多数组件/操作不同,线程安全即使是从另一个线程(即不是从EDT)进行重新绘制请求,所以实际绘画仅在EDT中发生.以下代码片段演示了这一点.

public class PaintingDemo {
 
    public static void main(String[] args) {
        final JFrame frame = new JFrame();
        final JPanel p = new MyPanel();
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                frame.add(p,BorderLayout.CENTER);
                frame.setSize(200,200);
                frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true);
            }
        });
        new Thread("MyThread") {
            public void run() {
                while (true) {
                // Below statements are important to show the difference
                    p.repaint();
                    p.paintImmediately(p.getBounds());
                    try {
                        Thread.sleep(1000);
                    } catch(Exception e) {}
                }
            }
        }.start();
    }
 
}
 
class MyPanel extends JPanel {
    @Override
    public void paint(Graphics g) {
        System.out.println("paint() called in "+ Thread.currentThread().getName());
        super.paint(g);
    }
}

从输出中可以看出,在调用repaint()时,在EDT中完成绘制,而不管调用哪个线程 – 所以没有问题.但是,在paintImmediately()的情况下 – 绘画发生在调用它的同一个线程中.

考虑一个情况是,EDT正在更改组件的状态,另一个线程(从中调用paintImmediately())正在绘制相同的组件.

我的问题：
在paintImmediately()的情况下,Event Dispatcher Thread(EDT)和其他线程之间的同步处理如何？

解决方法

据我了解,当您调用paintImmediately时,您调用以下代码：

Component c = this;
        Component parent;
 
        if(!isShowing()) {
            return;
        }
 
        JComponent paintingOigin = SwingUtilities.getPaintingOrigin(this);
        if (paintingOigin != null) {
            Rectangle rectangle = SwingUtilities.convertRectangle(
                    c,new Rectangle(x,y,w,h),paintingOigin);
            paintingOigin.paintImmediately(rectangle.x,rectangle.y,rectangle.width,rectangle.height);
            return;
        }
 
        while(!c.isOpaque()) {
            parent = c.getParent();
            if(parent != null) {
                x += c.getX();
                y += c.getY();
                c = parent;
            } else {
                break;
            }
 
            if(!(c instanceof JComponent)) {
                break;
            }
    }
    if(c instanceof JComponent) {
        ((JComponent)c)._paintImmediately(x,h);
    } else {
        c.repaint(x,h);
    }

所以,除非这不是一个JComponent,否则你最终会调用_paintImmediately(),最后调用paint(Graphics),建议下面的栈跟踪(从我将在这篇文章结尾发贴的一段代码中获取)：

Thread [pool-1-thread-1] (Suspended)    
    TestPaint$1.paint(Graphics) line: 23    
    TestPaint$1(JComponent).paintToOffscreen(Graphics,int,int) line: 5221 
    RepaintManager$PaintManager.paintDoubleBuffered(JComponent,Image,Graphics,int) line: 1482 
    RepaintManager$PaintManager.paint(JComponent,JComponent,int) line: 1413  
    RepaintManager.paint(JComponent,int) line: 1206   
    TestPaint$1(JComponent)._paintImmediately(int,int) line: 5169    
    TestPaint$1(JComponent).paintImmediately(int,int) line: 4980 
    TestPaint$1(JComponent).paintImmediately(Rectangle) line: 4992  
    TestPaint$3.run() line: 50  
    ThreadPoolExecutor.runWorker(ThreadPoolExecutor$Worker) line: 1110  
    ThreadPoolExecutor$Worker.run() line: 603   
    Thread.run() line: 722

但是如果您尝试同时调用repaint()(从另一个线程),您会看到它们同时运行(我尝试使用调试器执行代码并绘画从未停止在另一个线程中发生)似乎在Java代码级别,没有太多同步(至少我找不到任何东西).所以如果你最后在EDT中修改组件状态,我相信结果是不可预测的,你应该一定要避免这种情况.

为了说明我的观点,我尝试在paint方法中修改一个变量的状态,添加一个睡眠以增加2个线程(EDT和另一个线程)之间的冲突风险,并且它看起来似乎没有两者之间的同步线程(System.err.println()不时输出为null).

现在我想知道为什么你需要立即执行一个paint.除非你阻止EDT,否则没有太多有效的理由来执行这样的事情.

以下是我用来测试这些东西的代码(非常接近问题中的一个).代码只是为了尝试了解发生了什么,而不是展示如何执行正确的绘画或任何好的Swing练习.

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Random;
import java.util.concurrent.Executors;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
 
public class TestPaint {
 
    protected void initUI() {
        JFrame frame = new JFrame();
        frame.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
        frame.setTitle(TestPaint.class.getSimpleName());
        final Random rand = new Random();
        final JPanel comp = new JPanel() {
            private String value;
 
            @Override
            public void paint(Graphics g) {
                value = "hello";
                super.paint(g);
                try {
                    Thread.sleep(20);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                g.setColor(new Color(rand.nextInt(256),rand.nextInt(256),rand.nextInt(256)));
                g.fillRect(0,getWidth(),getHeight());
                if (SwingUtilities.isEventDispatchThread()) {
                    System.err.println("Painting in the EDT " + getValue());
                } else {
                    System.err.println("Not painting in EDT " + getValue());
                }
                value = null;
            }
 
            public String getValue() {
                return value;
            }
        };
        frame.add(comp);
        frame.setSize(400,400);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        Timer t = new Timer(1,new ActionListener() {
 
            @Override
            public void actionPerformed(ActionEvent e) {
                comp.repaint();
            }
        });
        t.start();
        Executors.newSingleThreadExecutor().execute(new Runnable() {
 
            @Override
            public void run() {
                while (true) {
                    comp.paintImmediately(comp.getBounds());
                }
            }
        });
    }
 
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new TestPaint().initUI();
            }
        });
    }
 
}

JComponent.paintImmediately()如何在Java Swing中运行？

解决方法

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