程序未访问扩展JPanel类的paintComponent()方法。

Question

这是JFrame。

package client.connection;

import java.awt.Dimension;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import javax.swing.JFrame;


class DrawFrameRemoteControl extends JFrame
{
    private DrawPanelRemoteControl imagePanel;
    private ClientRemoteControlConnection clientRemoteControlConnection;
    private ObjectInputStream clientInputStream;
    private ObjectOutputStream clientOutputStream;
    private Dimension imageDimension;
    private Dimension serverDimension;

    public DrawFrameRemoteControl(Dimension imageDimension,ClientRemoteControlConnection clientRemoteControlConnection,ObjectInputStream clientInputStream,ObjectOutputStream clientOutputStream,Dimension serverDimension)
    {
        super("Remote Desktop Control");

        this.clientRemoteControlConnection=clientRemoteControlConnection;
        this.clientInputStream=clientInputStream;
        this.clientOutputStream=clientOutputStream;
        this.imageDimension=imageDimension;
        this.serverDimension=serverDimension;

        imagePanel=new DrawPanelRemoteControl(imageDimension);
        add(imagePanel);


        setSize(imageDimension.width,imageDimension.height);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setVisible(true);
        setLocationRelativeTo(null);
    }

    void drawNewImageGrayscale(byte[] array)
    {
        imagePanel.setNewImageGrayscale(array);
        imagePanel.repaint();
    }
}

这是扩展了的JPanel类 -

package client.connection;

import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.Transparency;
import java.awt.color.ColorSpace;
import java.awt.image.BufferedImage;
import java.awt.image.ColorModel;
import java.awt.image.ComponentColorModel;
import java.awt.image.DataBuffer;
import java.awt.image.DataBufferByte;
import java.awt.image.MemoryImageSource;
import java.awt.image.Raster;
import java.awt.image.SampleModel;
import java.awt.image.WritableRaster;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;

class DrawPanelRemoteControl extends JPanel
{
    private byte[] byteArray=null;
    private Image image;
    private JLabel imageLabel=new JLabel();
    private Dimension imageDimension;

    public DrawPanelRemoteControl(Dimension imageDimension)
    {
        this.imageDimension=imageDimension;
        add(imageLabel);
    }

    @Override
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        System.out.println(".");
        if(byteArray!=null)
        {
            image=getGrayscaleImageFromArray(byteArray,imageDimension.width,imageDimension.height);
            imageLabel.setIcon(new ImageIcon(image));
        }
    }

    private Image getGrayscaleImageFromArray(byte[] buffer, int width, int height)
    {
        ColorSpace cs = ColorSpace.getInstance(ColorSpace.CS_GRAY);
        int[] nBits = { 8 };
        ColorModel cm = new ComponentColorModel(cs, nBits, false, true,Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
        SampleModel sm = cm.createCompatibleSampleModel(width, height);
        DataBufferByte db = new DataBufferByte(buffer, width * height);
        WritableRaster raster = Raster.createWritableRaster(sm, db, null);
        BufferedImage result = new BufferedImage(cm, raster, false, null);
        return result;
    }

    void setNewImageGrayscale(byte[] array)
    {
        this.byteArray=array;
        this.intArray=null;
    }
}

我已经尝试过调试代码，即使imagePanel.repaint()被执行多次，程序也从未到达DrawPanelRemoteControl类的paintComponent()方法。

有人能否给我任何想法为什么会发生这种情况？这与imageDimension对象有关吗？

附加信息：在main()方法中，创建了一个DrawFrameRemoteControl对象，并且该对象的drawNewImageGrayscale(byte[] arr)方法每秒都从main()中更新。

- Jisan Mahmud

---

请问您能否发布您的main方法。 - Harmeet Singh

我尝试了你的代码，它运行良好...可能有其他问题。 - Harmeet Singh

在paintComponent方法中，永远不要改变组件的状态（例如通过设置子组件的图标间接地改变状态），也不要执行任何可能耗时的任务（例如加载图像）。请注意保持原意并尽可能使翻译更加通俗易懂。 - kleopatra

@kleopatra，我按照您所说的做了。但似乎主要问题是当从main()创建一个DrawFrameRemoteControl对象时，它可以正常工作，但当从另一个JFrame对象创建一个DrawFrameRemoteControl时，它没有正确初始化（文件菜单未显示，背景显示为白色，而通常是灰色，关闭按钮不起作用，当我点击它时什么也不会发生）。 - Jisan Mahmud

Answer 1

不太清楚为什么要传递byte[]，但看起来你想用灰色缩略图来更新组件的Icon。下面的示例从现有的示例图标创建灰度图标，并使用setIcon()进行更新。任何Image都可以采用类似的方法处理。还可参见此示例建议使用ColorConvertOp，以及此示例更新整个组件而不是图标。

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics2D;
import java.awt.GraphicsConfiguration;
import java.awt.GraphicsDevice;
import java.awt.GraphicsEnvironment;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.awt.image.ColorConvertOp;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JToggleButton;
import javax.swing.Timer;
import javax.swing.UIManager;

/**
 * @see https://dev59.com/OmfWa4cB1Zd3GeqPl_OJ#12228640
 * @see https://stackoverflow.com/a/7935040/230513
 */
public class GrayIcons extends JPanel {

    private List<Icon> list = new ArrayList<Icon>();
    private List<JToggleButton> buttons = new ArrayList<JToggleButton>();
    private Timer timer = new Timer(1000, new ActionListener() {

        @Override
        public void actionPerformed(ActionEvent e) {
            update();
        }
    });

    public GrayIcons() {
        this.setLayout(new GridLayout(1, 0));
        list.add(getGray(UIManager.getIcon("OptionPane.errorIcon")));
        list.add(getGray(UIManager.getIcon("OptionPane.informationIcon")));
        list.add(getGray(UIManager.getIcon("OptionPane.warningIcon")));
        list.add(getGray(UIManager.getIcon("OptionPane.questionIcon")));
        for (Icon icon : list) {
            JToggleButton jtb = new JToggleButton(icon);
            buttons.add(jtb);
            this.add(jtb);
        }
        timer.start();
    }

    private void update() {
        Collections.shuffle(list);
        int index = 0;
        for (JToggleButton b : buttons) {
            b.setIcon(list.get(index++));
        }
    }

    /**
     * @see https://dev59.com/y2025IYBdhLWcg3wvIgo
     * @see https://dev59.com/hk7Sa4cB1Zd3GeqP5KJn#3106550
     */
    private Icon getGray(Icon icon) {
        final int w = icon.getIconWidth();
        final int h = icon.getIconHeight();
        GraphicsEnvironment ge =
            GraphicsEnvironment.getLocalGraphicsEnvironment();
        GraphicsDevice gd = ge.getDefaultScreenDevice();
        GraphicsConfiguration gc = gd.getDefaultConfiguration();
        BufferedImage image = gc.createCompatibleImage(w, h);
        Graphics2D g2d = image.createGraphics();
        g2d.setPaint(new Color(0x00f0f0f0));
        g2d.fillRect(0, 0, w, h);
        icon.paintIcon(null, g2d, 0, 0);
        BufferedImage gray = new BufferedImage(w, h, BufferedImage.TYPE_BYTE_GRAY);
        ColorConvertOp op = new ColorConvertOp(
            image.getColorModel().getColorSpace(),
            gray.getColorModel().getColorSpace(), null);
        op.filter(image, gray);
        return new ImageIcon(gray);
    }

    private void display() {
        JFrame f = new JFrame("GrayIcons");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(this);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new GrayIcons().display();
            }
        });
    }
}

- trashgod