Update JProgressBar from new Thread

How can I update the JProgressBar.setValue(int) from another thread? My secondary goal is do it in the least amount of classes possible.

Here is the code I have right now:

// Part of the main class....
pp.addActionListener(
        new ActionListener(){
            public void actionPerformed(ActionEvent event){
                new Thread(new Task(sd.getValue())).start(); 
            }
        });

public class Task implements Runnable {
    int val;
    public Task(int value){
        this.val = value;
    }

    @Override
    public void run() {
        for (int i = 0; i <= value; i++){ // Progressively increment variable i 
            pbar.setValue(i); // Set value 
            pbar.repaint(); // Refresh graphics 
            try{Thread.sleep(50);} // Sleep 50 milliseconds 
            catch (InterruptedException err){} 
        } 
    }
}

pp is a JButton and starts the new thread when the JButton is clicked.

pbar is the JProgressBar object from the Main class.

How can I update its value?(progress)

The code above in run() cannot see the pbar.

Always obey swing's rule

Once a Swing component has been realized, all code that might affect or depend on the state of that component should be executed in the event-dispatching thread.

What you can do is to create an observer that will update your progress bar -such as - in this instance you want to show progress of data being loaded on click of a button. DemoHelper class implements Observable and sends updates to all observers on when certain percent of data is loaded. Progress bar is updated via public void update(Observable o, Object arg) {

class PopulateAction implements ActionListener, Observer {

    JTable tableToRefresh;
    JProgressBar progressBar;
    JButton sourceButton;
    DemoHelper helper;
    public PopulateAction(JTable tableToRefresh, JProgressBar progressBarToUpdate) {
        this.tableToRefresh = tableToRefresh;
        this.progressBar = progressBarToUpdate;
    }

    public void actionPerformed(ActionEvent e) {
        helper = DemoHelper.getDemoHelper();
        helper.addObserver(this);
        sourceButton = ((JButton) e.getSource());
        sourceButton.setEnabled(false);
        helper.insertData();
    }

    public void update(Observable o, Object arg) {
        progressBar.setValue(helper.getPercentage());
    }
}

Shameless plug: this is from source from my demo project Feel free to browse for more details.

You shouldn't do any Swing stuff outside of the event dispatch thread. To access this, you need to create a Runnable with your code in run, and then pass that off to SwingUtilities.invokeNow() or SwingUtilities.invokeLater(). The problem is that we need a delay in your JProgressBar checking to avoid jamming up the Swing thread. To do this, we'll need a Timer which will call invokeNow or later in its own Runnable. Have a look at http://www.javapractices.com/topic/TopicAction.do?Id=160 for more details.

There is need not to call pbra.repaint explicitly.
Update JProgressBar shall be done through GUI dispatch thread.

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        // Remember to make pbar final variable.
        pbar.setValue(i);
    }
});

来源：https://stackoverflow.com/questions/2726091/update-jprogressbar-from-new-thread

标签

java

multithreading

jprogressbar