Java swing、SwingWorker、进程栏不会更新

Question

我的 Swingworker 不会重新绘制我的进度条(我有 2 个类(class))。

这是我的文件下载器代码。它将下载百分比显示在进度栏中。

public class Downloader extends SwingWorker<String, Integer> {

 private String fileURL, destinationDirectory;
 private int fileTotalSize;

 public void DownloaderF(String file, String dir) {
    this.fileURL = file;
    this.destinationDirectory = dir;
 }

 @Override
 protected String doInBackground() throws Exception {
    try {
        URL url = new URL(fileURL);
        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
        String downloadedFileName = fileURL.substring(fileURL.lastIndexOf("/")+1);
        int filesize = httpConn.getContentLength();
        int responseCode = httpConn.getResponseCode();
        byte[] buffer = new byte[4096];
        int bytesRead = 0;
        int i = 0;
        int total = 0;
        BufferedInputStream in = new BufferedInputStream(httpConn.getInputStream());
        FileOutputStream fos = new FileOutputStream(destinationDirectory + File.separator + downloadedFileName);
        BufferedOutputStream bout = new BufferedOutputStream(fos,4096);
        while ((i=in.read(buffer,0,4096))>=0) {
            total = total + i;
            bout.write(buffer,0,i);
            fileTotalSize = (total * 100) / filesize;
            publish(fileTotalSize);
        }
        bout.close();
        in.close();
    } catch(FileNotFoundException FNFE) {
        System.out.print("HTTP: 404!");
    } catch (IOException ex) {
        Logger.getLogger(Downloader.class.getName()).log(Level.SEVERE, null, ex);
    }
    return null;
}

 @Override
 protected void process(List<Integer> chunks) {
    try {
        Skin barValue = new Skin(); 
        barValue.setBar(fileTotalSize);
        //System.out.print("PROCESS:" + fileTotalSize + "\n");
    } catch (Exception ex) {
        ex.printStackTrace();
    }
 }
}

这是我的按钮代码和进度条值更改方法:

private void LoginButtonActionPerformed(java.awt.event.ActionEvent evt) {                                            
    // TODO add your handling code here:
    // Дебаг
    Downloader downloadFile = new Downloader();
    downloadFile.DownloaderF("http://ipv4.download.thinkbroadband.com/100MB.zip", ".");
    downloadFile.execute();
}                                           

public void setBar(int Value) {
    DownloadBar.setValue(Value);
    DownloadBar.repaint();

    System.out.print("1\n");
}

将打印“1\n”，但进度条不会移动。

抱歉我的英语不好。

Answer 1

您的问题很可能来自这一行:

Skin barValue = new Skin();

您正在重新创建 Skin 类的新实例，而不是引用已存在的实例。因此，您很可能指向一些可能根本没有显示的东西，因此您看不到任何事情发生。

正确的方法是向您的类 Downloader 提供对包含显示的“进度条”的原始 Skin 的引用。

仅供引用:

• 当您更改 JProgressBar 的值时，无需调用 repaint()(进度条会为您执行此操作)
• 请遵循 Java 命名约定(即方法名称和变量必须以小写字母开头):对于有经验的用户来说，您的代码更难阅读。

这是从您的代码中派生的示例代码(尽管我做了一些快捷方式)，它实际上按预期正常工作:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.List;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JProgressBar;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

public class Skin {

    private JProgressBar DownloadBar;

    public static class Downloader extends SwingWorker<String, Integer> {

        private final String fileURL, destinationDirectory;
        private int fileTotalSize;
        private final Skin barValue;

        public Downloader(Skin skin, String file, String dir) {
            this.barValue = skin;
            this.fileURL = file;
            this.destinationDirectory = dir;
        }

        @Override
        protected String doInBackground() throws Exception {
            try {
                URL url = new URL(fileURL);
                HttpURLConnection httpConn = (HttpURLConnection) url
                        .openConnection();
                String downloadedFileName = fileURL.substring(fileURL
                        .lastIndexOf("/") + 1);
                int filesize = httpConn.getContentLength();
                int responseCode = httpConn.getResponseCode();
                byte[] buffer = new byte[4096];
                int bytesRead = 0;
                int i = 0;
                int total = 0;
                BufferedInputStream in = new BufferedInputStream(
                        httpConn.getInputStream());
                FileOutputStream fos = new FileOutputStream(
                        destinationDirectory + File.separator
                                + downloadedFileName);
                BufferedOutputStream bout = new BufferedOutputStream(fos, 4096);
                while ((i = in.read(buffer, 0, 4096)) >= 0) {
                    total = total + i;
                    bout.write(buffer, 0, i);
                    fileTotalSize = total * 100 / filesize;
                    publish(fileTotalSize);
                }
                bout.close();
                in.close();
            } catch (FileNotFoundException FNFE) {
                System.out.print("HTTP: 404!");
            } catch (IOException ex) {
                Logger.getLogger(Downloader.class.getName()).log(Level.SEVERE,
                        null, ex);
            }
            return null;
        }

        @Override
        protected void process(List<Integer> chunks) {
            barValue.setBar(fileTotalSize);
        }
    }

    private void loginButtonActionPerformed(java.awt.event.ActionEvent evt) {
        Downloader downloadFile = new Downloader(this,
                "http://ipv4.download.thinkbroadband.com/100MB.zip", ".");
        downloadFile.execute();
    }

    protected void initUI() throws MalformedURLException {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JButton login = new JButton("Login");
        login.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                loginButtonActionPerformed(e);
            }
        });
        DownloadBar = new JProgressBar();
        frame.add(login, BorderLayout.NORTH);
        frame.add(new JLabel(new ImageIcon(new URL(
                "http://home.scarlet.be/belperret/images/image1.jpg"))));
        frame.add(DownloadBar, BorderLayout.SOUTH);
        frame.pack();
        frame.setVisible(true);
    }

    public void setBar(int Value) {
        DownloadBar.setValue(Value);
        DownloadBar.repaint();

        System.out.println("1");
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    new Skin().initUI();
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                }
            }
        });
    }
}