java - Make a swing thread that show a "Please Wait" JDialog

Question

The problem is this:
I've a swing application running, at a certain point a dialog requires to insert username and password and to press "ok".
I would like that when the user press "ok" the swing application does in this order:

1. Open a "Please wait" JDialog
   
2. Make some operation(eventually displaying some other JDialog or JOptionPane)
   
3. When it finishes with the operation close the "please wait" JDialog
   

This is the code that I wrote in the okButtonActionPerformed():

private void okButtonActionPerformed(java.awt.event.ActionEvent evt) { 
    //This class simply extends a JDialog and contains an image and a jlabel (Please wait)
    final WaitDialog waitDialog = new WaitDialog(new javax.swing.JFrame(), false);    
    waitDialog.setVisible(true);
    ... //Do some operation (eventually show other JDialogs or JOptionPanes)
    waitDialog.dispose()
}

This code obviously doesn't works because when I call the waitDialog in the same thread it blocks all till I don't close it.
So I tried to run it in a different thread:

private void okButtonActionPerformed(java.awt.event.ActionEvent evt) { 
    //This class simply extends a JDialog and contains an image and a jlabel (Please wait)
    final WaitDialog waitDialog = new WaitDialog(new javax.swing.JFrame(), false);    
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            waitDialog.setVisible(true);
        }
    });
    ... //Do some operation (eventually show other JDialogs or JOptionPanes)
    waitDialog.dispose()
}

But also this doesn't work because the waitDialog is not displayed immediately but only after that the operation completed their work (when they show a joption pane "You are logged in as...")

I also tried to use invokeAndWait instead of invokeLater but in this case it throws an exception:

Exception in thread "AWT-EventQueue-0" java.lang.Error: Cannot call invokeAndWait from the event dispatcher thread

How can I do?

Answer 1

Consider using a SwingWorker to do your background work, and then closing the dialog either in the SwingWorker's done() method or (my preference) in a PropertyChangeListener that is added to the SwingWorker.

e.g.,

import java.awt.BorderLayout;
import java.awt.Dialog.ModalityType;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;    
import javax.swing.*;

public class PleaseWaitEg {
   public static void main(String[] args) {
      JButton showWaitBtn = new JButton(new ShowWaitAction("Show Wait Dialog"));
      JPanel panel = new JPanel();
      panel.add(showWaitBtn);
      JFrame frame = new JFrame("Frame");
      frame.getContentPane().add(panel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);

   }
}

class ShowWaitAction extends AbstractAction {
   protected static final long SLEEP_TIME = 3 * 1000;

   public ShowWaitAction(String name) {
      super(name);
   }

   @Override
   public void actionPerformed(ActionEvent evt) {
      SwingWorker<Void, Void> mySwingWorker = new SwingWorker<Void, Void>(){
         @Override
         protected Void doInBackground() throws Exception {

            // mimic some long-running process here...
            Thread.sleep(SLEEP_TIME);
            return null;
         }
      };

      Window win = SwingUtilities.getWindowAncestor((AbstractButton)evt.getSource());
      final JDialog dialog = new JDialog(win, "Dialog", ModalityType.APPLICATION_MODAL);

      mySwingWorker.addPropertyChangeListener(new PropertyChangeListener() {

         @Override
         public void propertyChange(PropertyChangeEvent evt) {
            if (evt.getPropertyName().equals("state")) {
               if (evt.getNewValue() == SwingWorker.StateValue.DONE) {
                  dialog.dispose();
               }
            }
         }
      });
      mySwingWorker.execute();

      JProgressBar progressBar = new JProgressBar();
      progressBar.setIndeterminate(true);
      JPanel panel = new JPanel(new BorderLayout());
      panel.add(progressBar, BorderLayout.CENTER);
      panel.add(new JLabel("Please wait......."), BorderLayout.PAGE_START);
      dialog.add(panel);
      dialog.pack();
      dialog.setLocationRelativeTo(win);
      dialog.setVisible(true);
   }
}

Notes:

• A key concept is to set everything up, add the PropertyChangeListener, get the SwingWorker running, all before displaying the modal dialog, because once the modal dialog is shown, all code flow from the calling code is frozen (as you've found out).
• Why do I prefer the PropertyChangeListener to using the done method (as Elias demonstrates in his decent answer here, which I've up-voted) -- using the listener provides more separation of concerns, looser coupling. This way the SwingWorker has to know nothing of the GUI code that is using it.