从另一个类设置Progressbar

Question

I'm trying to set my progressbar from another class but failed. This is my progressbar the class Upload .

JProgressBar progressBar = new JProgressBar();
progressBar.setBounds(91, 134, 284, 17);
frame.getContentPane().add(progressBar);

I have another class called Read . In this class I have a loop that needs to read a file, so I want to set the progress with the iterator i from that class. I know that I have to set the minimum and maxium like this:

progressBar.setMinimum(0);
progressBar.setMaximum(numRows);

And for the value:

progressBar.setValue(newValue);

How can I set the value for the progressbar so it keeps updating the value of i ?

Answer 1

First of all, your Reader class must have a reference to the component (JProgressBar) in question. I understand that this is already solved.

After that, for reading a file I strongly recommend to use a class extending javax.swing.SwingWorker . That pattern allows you to work in background (may be for heavy operations like reading big files) without affecting the AWT thread, so your GUI won't be affected. So, your reader should extend javax.swing.SwingWorker .

As a brief resume, it provides a method called doInBackground where you should implement the 'heavy' operation and also a method called process where it is received the data chunks and you add your own calculations for the progress.

The process method is executed in AWT, so you can update any UI Component at this method (so a good point to update your progress bar)

Please, refer to this link for more information.

Answer 2

You should use SwingWorker for it as described in the JProgressBar documentation .

This SwingWorker is a thread on which we can add a propertyChangeListener

After which we can call firePropertyChange to invoke the listener. In the listener we can update the progress bar by calling setValue() on it.

Following is a working example of reading a file and updating the progress bar.

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JProgressBar;
import javax.swing.SwingWorker;

public class ProgressBar {

    private static final String PROGRESS_PROPERTY_NAME = "progress";
    final static String fileName = "My_file_location";

    public static void main(String[] args) {
        JFrame frame = new JFrame("Progress bar");
        JPanel panel = new JPanel();

        final JProgressBar progressBar = new JProgressBar();
        progressBar.setMinimum(0);
        progressBar.setMaximum(100);
        progressBar.setStringPainted(true);

        panel.add(progressBar);


        JButton button = new JButton("Start reading");
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                ReadFiletask task = new ReadFiletask(fileName);
                 task.addPropertyChangeListener(
                 new PropertyChangeListener() {
                     public  void propertyChange(PropertyChangeEvent evt) {

                         if (PROGRESS_PROPERTY_NAME.equals(evt.getPropertyName())) {
                             progressBar.setValue((Integer)evt.getNewValue());
                         }
                     }
                 });

                 task.execute();
            }
        });
        panel.add(button);

        frame.add(panel);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.setVisible(true);
    }

    public static class ReadFiletask extends SwingWorker<Boolean, Integer> {
        String fileName;
        public ReadFiletask (String fileName) {
            this.fileName = fileName;
        }

        @Override
        protected Boolean doInBackground() throws Exception {
            System.out.println("Started reading");
            byte[] buffer = new byte[1024 * 1024];//1mb
            InputStream is = null;
            try {
                Path file = Paths.get(fileName);
                long fileSize = Files.size(file);
                is = Files.newInputStream(file, StandardOpenOption.READ);
                int readLen = -1;
                int readCounter = 0;
                while((readLen = is.read(buffer)) != -1) {
                    readCounter += readLen;

                    int percentDone = (int)( (readCounter * 100.0) / fileSize);
                    System.out.println("done : " + percentDone);

                    /*Most important part is here */

                    firePropertyChange(PROGRESS_PROPERTY_NAME, 0, percentDone);
                }

            } catch (IOException e1) {
                e1.printStackTrace();
            } finally {
                if(is != null) {
                    try {
                        is.close();
                    } catch (IOException e1) {
                        e1.printStackTrace();
                    }
                }
            }
            System.out.println("Finished");
            return true;
        }

    }
}