Can you use publish from a method called in run in background?

Question

I am using swingworker to run a method in the background and periodically update the gui with information, but from what I've found publish can't be called from another class. Here's where my Swingworker is called:

private void start() {
    worker = new SwingWorker <Void, String>() {

        @Override
        protected Void doInBackground() throws Exception {
            navigator.navigator();

            return null;
        }
        @Override
        protected void process(List<String> chunks) {
            for (String line : chunks) {
                txtrHello.append(line);
                txtrHello.append("\n");
            }
        }
        @Override
        protected void done() {

        }

    };
    worker.execute();
}

And now from the navigator method I want to call publish(String);, how would I do this? Moving all of my methods into doInBackground() would be impossible.

Answer 1

Possible solution is to add an observer to your Navigator object, the key being to somehow allow the Navigator to communicate with any listener (here the SwingWorker) that its state has changed:

• Give Navigator a PropertyChangeSupport object as well as an addPropertyChangeListener(PropertyChangeListener listener) method that adds the passed in listener to the support object.
• Give Navigator some type of "bound" property, a field that when its state is changed, often in a setXxxx(...) type method, notifies the support object of this change.
• Then in your SwingWorker constructor, add a PropertyChangeListener to your Navigator object.
• In this listener, call the publish method with the new data from your Navigator object.

---

For example:

import java.awt.event.ActionEvent;
import java.beans.*;
import java.util.List;
import javax.swing.*;

@SuppressWarnings("serial")
public class PropChangeSupportEg extends JPanel {
   private MyNavigator myNavigator = new MyNavigator();
   private JTextField textField = new JTextField(10);

   public PropChangeSupportEg() {
      textField.setFocusable(false);
      add(textField);
      add(new JButton(new StartAction("Start")));
      add(new JButton(new StopAction("Stop")));
   }

   private class StartAction extends AbstractAction {
      public StartAction(String name) {
         super(name);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         if (myNavigator.isUpdatingText()) {
            return; // it's already running
         }
         MyWorker worker = new MyWorker();
         worker.execute();
      }
   }

   private class StopAction extends AbstractAction {
      public StopAction(String name) {
         super(name);
      }

      @Override
      public void actionPerformed(ActionEvent e) {
         myNavigator.stop();
      }
   }

   private class MyWorker extends SwingWorker<Void, String> {
      @Override
      protected Void doInBackground() throws Exception {
         if (myNavigator.isUpdatingText()) {
            return null;
         }

         myNavigator.addPropertyChangeListener(new PropertyChangeListener() {

            @Override
            public void propertyChange(PropertyChangeEvent evt) {
               if (MyNavigator.BOUND_PROPERTY_TEXT.equals(evt.getPropertyName())) {
                  publish(evt.getNewValue().toString());
               }
            }
         });
         myNavigator.start();
         return null;
      }

      @Override
      protected void process(List<String> chunks) {
         for (String chunk : chunks) {
            textField.setText(chunk);
         }
      }


   }

   private static void createAndShowGui() {
      PropChangeSupportEg mainPanel = new PropChangeSupportEg();

      JFrame frame = new JFrame("Prop Change Eg");
      frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
      frame.getContentPane().add(mainPanel);
      frame.pack();
      frame.setLocationByPlatform(true);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGui();
         }
      });
   }
}

class MyNavigator {
   public static final String BOUND_PROPERTY_TEXT = "bound property text";
   public static final String UPDATING_TEXT = "updating text";
   private static final long SLEEP_TIME = 1000;
   private PropertyChangeSupport pcSupport = new PropertyChangeSupport(this);
   private String boundPropertyText = "";
   private String[] textArray = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};
   private int textArrayIndex = 0;
   private volatile boolean updatingText = false;

   public void start() {
      if (updatingText) {
         return;
      }
      updatingText = true;
      while (updatingText) {
         textArrayIndex++;
         textArrayIndex %= textArray.length;
         setBoundPropertyText(textArray[textArrayIndex]);
         try {
            Thread.sleep(SLEEP_TIME);
         } catch (InterruptedException e) {}
      }
   }

   public void stop() {
      setUpdatingText(false);
   }

   public String getBoundPropertyText() {
      return boundPropertyText;
   }

   public boolean isUpdatingText() {
      return updatingText;
   }

   public void setUpdatingText(boolean updatingText) {
      boolean oldValue = this.updatingText;
      boolean newValue = updatingText;
      this.updatingText = updatingText;
      pcSupport.firePropertyChange(UPDATING_TEXT, oldValue, newValue);
   }

   public void setBoundPropertyText(String boundPropertyText) {
      String oldValue = this.boundPropertyText;
      String newValue = boundPropertyText;
      this.boundPropertyText = boundPropertyText;
      pcSupport.firePropertyChange(BOUND_PROPERTY_TEXT, oldValue, newValue);
   }

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

   public void removePropertyChangeListener(PropertyChangeListener listener) {
      pcSupport.removePropertyChangeListener(listener);
   }
}