JProgressBar不会更新

问题描述

我正在尝试在此问题的投票答案中找到的代码：

I'm trying the code I found on the voted answer from this question: Download file using java apache commons?

这是一个下载应用程序，看一看，（我对JFrames和ActionEvents不太熟悉）

It's a download application, take a little look, (I'm not much familiar with JFrames and ActionEvents)

Download.java

Download.java

package main;

public class Download extends JFrame implements Runnable{

    public static int total;
    public static int done;

    private static class ProgressListener implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {

            done = (int)((DownloadCountingOutputStream) e.getSource()).getByteCount();
            jbar.repaint();
            DownloadCountingOutputStream.parent.draw((int)((DownloadCountingOutputStream) e.getSource()).getByteCount());//redraw
            DownloadCountingOutputStream.parent.repaint();
        }
    }

    public static JProgressBar jbar = new JProgressBar();



    public void draw(int downloaded){System.out.println("downloaded: "+downloaded+ " Total: "+total);

        if (downloaded== 0){

        Container cont = new Container();
        setDefaultCloseOperation(3);
        setSize(600, 450);
        setResizable(false);
        setVisible(true);

        cont.add(jbar);
        jbar.setBounds(40, 50, 500, 50);
        jbar.setMaximum(total);//The total value of bytes to download
        //jbar.setValue(50);
        add(cont);

        jbar.setVisible(true);
        }

        jbar.setValue(downloaded);
            //This should update the value of the progress Bar
    }

    public void run() {


        URL dl = null;
        File fl = null;
        OutputStream os = null;
        InputStream is = null;
        ProgressListener progressListener = new ProgressListener();

        draw(done);

        try {
            fl = new File(System.getProperty("user.home").replace("\\", "/") + "/Desktop/afile.rar");
            dl = new URL("https://dl.dropbox.com/u/48076798/afile.rar");
            os = new FileOutputStream(fl);
            is = dl.openStream();

            total = Integer.parseInt(dl.openConnection().getHeaderField("Content-Length"));

            String total = dl.openConnection().getHeaderField("Content-Length");

            DownloadCountingOutputStream dcount = new DownloadCountingOutputStream(os);
            dcount.setListener(progressListener);
            dcount.setParent(this);

            IOUtils.copy(is, dcount);

        } catch (Exception e) {
            System.out.println(e);
        } finally {
            if (os != null) {
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (is != null) {
                try {
                    is.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

DownloadCountingOutputStream.java

DownloadCountingOutputStream.java

package main;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.io.OutputStream;

import org.apache.commons.io.output.CountingOutputStream;

public class DownloadCountingOutputStream extends CountingOutputStream {

    private ActionListener listener = null;
    public static Download parent;

    public DownloadCountingOutputStream(OutputStream out) {
        super(out);
    }

    public void setListener(ActionListener listener) {
        this.listener = listener;
    }

    public void setParent(Download o){

        parent = o;
    }

    @Override
    protected void afterWrite(int n) throws IOException {
        super.afterWrite(n);
        if (listener != null) {
            listener.actionPerformed(new ActionEvent(this, 0, null));
        }
    }

}

推荐答案

从您提供的代码示例中很难说明...

It's difficult to tell from the code sample you've provide...

此问题的主要原因是尝试更新UI阻止事件调度线程（EDT）。

The main cause of this problem is trying to update the UI while blocking from the Event Dispatching Thread (EDT).

重要的是不要在EDT中执行任何长时间运行或阻塞操作，因为这样可以防止重绘请求被执行。

It's important to NEVER do any long running or blocking operations within the EDT as this will prevent repaint requests from been acted upon.

欲了解更多信息，请阅读

For more information have a read through Concurrency in Swing

以下示例演示了如何使用 SwingWorker 提供与UI重新同步的进度更新

The example below demonstrates the use of a SwingWorker that provides progress updates that are re-synced with the UI

public class TestProgress {

    public static void main(String[] args) {
        new TestProgress();
    }

    public TestProgress() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                ProgressPane progressPane = new ProgressPane();
                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(progressPane);
                frame.setSize(200, 200);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);

                progressPane.doWork();
            }
        });
    }

    public class ProgressPane extends JPanel {

        private JProgressBar progressBar;

        public ProgressPane() {

            setLayout(new GridBagLayout());
            progressBar = new JProgressBar();

            add(progressBar);

        }

        public void doWork() {

            Worker worker = new Worker();
            worker.addPropertyChangeListener(new PropertyChangeListener() {
                @Override
                public void propertyChange(PropertyChangeEvent evt) {
                    if ("progress".equals(evt.getPropertyName())) {
                        progressBar.setValue((Integer) evt.getNewValue());
                    }
                }
            });

            worker.execute();

        }
    }

    public class Worker extends SwingWorker<Object, Object> {

        @Override
        protected Object doInBackground() throws Exception {

            for (int index = 0; index < 1000; index++) {
                int progress = Math.round(((float) index / 1000f) * 100f);
                setProgress(progress);

                Thread.sleep(10);
            }

            return null;
        }
    }
}

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