Question

I am working on an application that executes some functions that run for long. To let the user aware that the processing is taking place, I needed a label that can display some label that can represent that. So, I created a small widget for such a label.

The program below runs find and I get the output as I wanted.

import java.awt.Dimension;
import java.util.ArrayList;
import java.util.List;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;


/**
 * This is an extension to a JLabel that can be used to display an ongoing progress.
 * @author Ankit Gupta
 */
public class ProgressLabel extends JLabel {

    /**
     * The prefix label to which periods are added.
     */
    private String startLabel;
    /**
     * The label to display end of an operation.
     */
    private String endLabel;

    /**
     * Flag to indicate whether the animation is running or not.
     */
    private boolean running = false;
    //list to hold intermediate labels
    List<String> intermediateLabels;

    public ProgressLabel(String slbl, String elbl) {
        this.startLabel = slbl;
        this.endLabel = elbl;
        //initialize all the labels to be used once as creating them again and again is expensive
        intermediateLabels = new ArrayList<String>();
        intermediateLabels.add(startLabel+".");
        intermediateLabels.add(startLabel+"..");
        intermediateLabels.add(startLabel+"...");
        intermediateLabels.add(startLabel+"....");
    }

    public void done(){
        running = false;
    }

    public void start(){
        running = true;
        new LabelUpdateThread().start();
    }

    private class LabelUpdateThread extends Thread{
        int i;

        public LabelUpdateThread(){
            i=0;
        }

        @Override
        public void run(){
            while(running){
                SwingUtilities.invokeLater(new Runnable(){
                    @Override
                    public void run() {
                        setText(intermediateLabels.get((i++)%3));
                    }
                });

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException ex) {}
            }
            setText(endLabel);
        }
    }

    public static void main(String []args) throws InterruptedException{
        final JFrame frame = new JFrame("Testing ProgressLabel");
        JPanel panel = new JPanel();
        ProgressLabel progressLabel = new CZProgressLabel("Searching", "Done");
        panel.add(progressLabel);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(500,500));
        frame.pack();
        progressLabel.start();
        SwingUtilities.invokeLater(new Runnable(){
            @Override
            public void run() {
                frame.setVisible(true);
            } 
        });
        Thread.sleep(5000);
        progressLabel.done();
    }
}

However, when I tried to include this in the application, it did not work as expected. I created a small panel with a button and in the actionPerfomed() code for the button I used the ProgressLabel‘s start() and done() methods as before but this time, the label just did not update to Done until the length process finished. Here is another piece of code using the ProgressLabel with actionPerformed() :

public class SearchPanel extends JPanel {

    private JTextArea queryBox;
    private JButton searchBtn;
    private ProgressLabel progressLabel;
    private JSeparator queryAreaSeparator;

    public SearchPanel() {
        setLayout(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();

        //First Row
        gbc.gridy = 0;
        gbc.gridwidth = 2;
        gbc.gridx = 0;
        queryBox = new JTextArea();
        queryBox.setRows(25);
        queryBox.setColumns(25);
        this.add(queryBox, gbc);


        //Second Row
        gbc.gridy = 1;

        gbc.gridwidth = 1;
        progressLabel = new ProgressLabel("Searching", "Done");
        this.add(progressLabel, gbc);

        gbc.gridx = 1;
        searchBtn = new JButton("Search");
        this.add(searchBtn, gbc);
        searchBtn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                progressLabel.start();
                try {
                    Thread.sleep(10000);
                } catch (InterruptedException ex) {
                    Exceptions.printStackTrace(ex);
                }
                //the above sleep() call will be replace by some time-consuming process. It is there just for testing now

                progressLabel.done();
            }
        });


        gbc.gridx = 0;
    }

    /**
     * function to test CZSemanticSearchLabel
     */
    public static void main(String[] args) throws InterruptedException {
        final JFrame frame = new JFrame();
        CZSemanticSearchPanel panel = new CZSemanticSearchPanel();
        frame.add(panel);
        frame.setPreferredSize(new Dimension(500, 500));
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        Thread.sleep(10000);
        frame.dispose();


        final JFrame frame1 = new JFrame("Testing ProgressLabel");
        JPanel panel1 = new JPanel();
        CZProgressLabel progressLabel = new CZProgressLabel("Searching", "Done");
        panel1.add(progressLabel);
        frame1.add(panel1);
        frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame1.setPreferredSize(new Dimension(500, 500));
        frame1.pack();
        progressLabel.start();
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                frame1.setVisible(true);
            }
        });
        Thread.sleep(5000);
        progressLabel.done();
    }
}

I believe that I have screwed something with Swing’s Event dispatch model. But, I cannot figure what? Can someone tell me what is wrong with this code and how do I correct it?

Answer 1

I don’t know about your actual code, but your sample code is flawed…

In your ActionListener you are doing this…

progressLabel.start();
try {
    Thread.sleep(10000);
} catch (InterruptedException ex) {
    Exceptions.printStackTrace(ex);
}
//the above sleep() call will be replace by some time-consuming process. It is there just for testing now

progressLabel.done();

This will STOP the Event Dispatching Thread, preventing any repaint requests from the been handled (ie no screen updates) for 10 seconds…this will also make your application look like it’s “hung”.

I updated you ActionListener to read like this (note I added a isRunning method which returns the running member from the label)

if (progressLabel.isRunning()) {
    progressLabel.done();
} else {
    progressLabel.start();
}

And it works fine.

You might like to read through Currency in Swing for some more ideas.

Also, as already suggested, SwingWorker may be a better approach