MVC Progress Bar Threading

Question

I am using an MVC pattern for my design, when a user presses the search button, I call a search in the model, but I also want to update a progress bar with information returned from that model.

I have tried using a swingworker, but the progress bar does not update. I suspect I am doing something wrong with my threading.

My button as defined in the controller is:

 class SearchBtnListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            _view.displayProgress();  
        }    
}

This calls the search in the model and has the following call in the view:

public void displayProgress() {

    TwoWorker task = new TwoWorker();
    task.addPropertyChangeListener(new PropertyChangeListener() {

         @Override
         public void propertyChange(PropertyChangeEvent e) {
             if ("progress".equals(e.getPropertyName())) {
                _progressBar.setValue((Integer) e.getNewValue());
             }
         }

     });
     task.execute();             
}      


private class TwoWorker extends SwingWorker<Void, Void> {        
    @Override
    protected Void doInBackground() throws Exception {
        _model.startSearch(getTerm());                  // time intensive code
        File file = new File("lock");           
        while (file.exists()){
            setProgress(_model.getStatus());
            System.out.println(_model.getStatus()); // never called
        }           
        return null;
    }  

    protected void done(){
        updateMain();
    }
}

Dummy function defined in Model for testing:

public int getStatus(){
    Random r = new Random();
    return r.nextInt();
}

Answer 1

Don't call

_progressBar.setValue(_model.getStatus());

from within your SwingWorker as this is calling Swing code from a background thread and is what the PropertyChangeListener is for anyway. Instead, just set the progress property, that's all.

Also, don't call done() from within the doInBackground method as this needs to be called from the EDT by the SwingWorker. So let the SwingWorker itself call this method when it is in fact done.

Also, Done() should be done() -- the first letter shouldn't be capitalized, and you should use @Override annotations in this code so you can be sure that you're overriding methods correctly.

Also, what does this do?

 _model.startSearch(_view.getTerm());

Does it call code that takes a while to complete? Should this be initialized from within the SwingWorker doInBackground itself?

Edit: Another option is to give the Model a bound int property, say called progress, and then add a PropertyChangeListener to it directly letting it update the JProgressBar. For example,

import java.awt.BorderLayout;
import java.awt.event.*;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import java.beans.PropertyChangeSupport;

import javax.swing.*;

public class MVC_ProgressBarThread {
   private static void createAndShowUI() {
      MVC_View view = new MVC_View();
      MVC_Model model = new MVC_Model();
      MVC_Control control = new MVC_Control(view, model);
      view.setControl(control);

      JFrame frame = new JFrame("MVC_ProgressBarThread");
      frame.getContentPane().add(view);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      java.awt.EventQueue.invokeLater(new Runnable() {
         public void run() {
            createAndShowUI();
         }
      });
   }
}

@SuppressWarnings("serial")
class MVC_View extends JPanel {
   private MVC_Control control;
   private JProgressBar progressBar = new JProgressBar();
   private JButton startActionButton = new JButton("Start Action");

   public MVC_View() {
      startActionButton.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            buttonActionPerformed();
         }
      });

      JPanel buttonPanel = new JPanel();
      buttonPanel.add(startActionButton);
      setLayout(new BorderLayout());
      add(buttonPanel, BorderLayout.NORTH);
      add(progressBar, BorderLayout.CENTER);
   }

   public void setControl(MVC_Control control) {
      this.control = control;
   }

   private void buttonActionPerformed() {
      if (control != null) {
         control.doButtonAction();
      }
   }

   public void setProgress(int progress) {
      progressBar.setValue(progress);
   }

   public void start() {
      startActionButton.setEnabled(false);
   }

   public void done() {
      startActionButton.setEnabled(true);
      setProgress(100);
   }
}

class MVC_Control {
   private MVC_View view;
   private MVC_Model model;

   public MVC_Control(final MVC_View view, final MVC_Model model) {
      this.view = view;
      this.model = model;
      model.addPropertyChangeListener(new PropertyChangeListener() {
         public void propertyChange(PropertyChangeEvent pce) {
            if (MVC_Model.PROGRESS.equals(pce.getPropertyName())) {
               view.setProgress((Integer)pce.getNewValue());
            }
         }
      });
   }

   public void doButtonAction() {
      view.start();
      SwingWorker<Void, Void> swingworker = new SwingWorker<Void, Void>() {
         @Override
         protected Void doInBackground() throws Exception {
            model.reset();
            model.startSearch();
            return null;
         }

         @Override
         protected void done() {
            view.done();
         }
      };
      swingworker.execute();
   }

}

class MVC_Model {
   public static final String PROGRESS = "progress";
   private static final int MAX = 100;
   private static final long SLEEP_DELAY = 100;
   private int progress = 0;
   private PropertyChangeSupport pcs = new PropertyChangeSupport(this);

   public void setProgress(int progress) {
      int oldProgress = this.progress;
      this.progress = progress;

      PropertyChangeEvent evt = new PropertyChangeEvent(this, PROGRESS, oldProgress, progress);
      pcs.firePropertyChange(evt);
   }

   public void reset() {
      setProgress(0);
   }

   public void addPropertyChangeListener(PropertyChangeListener listener) {
      pcs.addPropertyChangeListener(listener);
   }

   public void startSearch() {
      for (int i = 0; i < MAX; i++) {
         int newValue = (100 * i) / MAX;
         setProgress(newValue);
         try {
            Thread.sleep(SLEEP_DELAY);
         } catch (InterruptedException e) {}
      }
   }
}