Help to call a method on dispose()

Hey.

Basically what I want to do is call a method when clicking on the close button in the JFrame (the default one in the top corner).

I don't know if it's possible to override the DISPOSE_ON_CLOSE - or if it's the easiest to do.

Anyway, I'll give you a few stumps of code:

MainFrame:

Code:

---

package gui;
import ...

public class MainFrame extends JFrame {

        private JButton btnAdmConf;

        private Controller controller;

        public MainFrame() {
                ...
                this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                ...

                controller = new Controller();

                ...

                refreshButtons();

                this.setVisible(true);
        }

        public void refreshButtons() {
                ...
        }

        public JFrame getFrame() {
                return this;
        }

        private class Controller implements ActionListener
        {
                public void actionPerformed(ActionEvent e){
                        if (e.getSource() == btnAdmConf) {
                                new ConferenceFrame(getFrame());
                        }
                }
        }
}

---

And...

ConferenceFrame:

Code:

---

package gui;
import ...

public class ConferenceFrame extends JFrame{

        private MainFrame fromFrame;
        private Controller controller;


        public ConferenceFrame(JFrame fromFrame)
        {
                ...
                this.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                ...
                this.fromFrame = (MainFrame)fromFrame;
                ...
                controller = new Controller();
                ...
                this.setVisible(true);
        }
       
        public MainFrame getFromFrame() {
                return fromFrame;
        }

        public JFrame getFrame() {
                return this;
        }

        private class Controller implements ActionListener
        {
                public void actionPerformed(ActionEvent e){
                        ...
                }
        }

}

---

Sorry if I wrote any incorrect brackets - ignore it if you can.
So, on my my ConferenceFrame, I want to call getFromFrame.refreshButtons() when I dispose the frame.

Any suggestions?

Quote:

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Originally Posted by Muskar

So, on my my ConferenceFrame, I want to call getFromFrame.refreshButtons() when I dispose the frame.

Any suggestions?

---

Yup, override the dispose() method in your class (make it call the superclass dispose() method when it has done its job), i.e. in your class:

Code:

---

public void dispose() {
  // do your work here
  super.dispose();
}

---

kind regards,

Jos

Nice! It worked right away. Thanks a lot, Jos :)

Quote:

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Yup, override the dispose() method in your class

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Sorry, Jos, but I consider this a wrong approach.

I would go with a WindowListener#windowClosing.
How to Write Window Listeners (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listeners)

db

Quote:

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Originally Posted by Darryl.Burke

Sorry, Jos, but I consider this a wrong approach.

I would go with a WindowListener#windowClosing.
How to Write Window Listeners (The Java™ Tutorials > Creating a GUI With JFC/Swing > Writing Event Listeners)

db

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As far as I understand - there's no actual difference.
Except, logically, I would guess that adding another listener requires a tiny bit more memory than just overriding a method.

Could you perhaps enlighten your reasons for your opinion?

Quote:

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Originally Posted by Darryl.Burke

Sorry, Jos, but I consider this a wrong approach. I would go with a WindowListener#windowClosing.

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Yep, that's the gentle way to do it; come to think of it: if one of those listeners later in the chain bails out (e.g. by throwing an Exception) the window won't be closed or disposed while our own listener assumed it would ...

kind regards,

Jos

Quote:

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Originally Posted by JosAH

Yep, that's the gentle way to do it; come to think of it: if one of those listeners later in the chain bails out (e.g. by throwing an Exception) the window won't be closed or disposed while our own listener assumed it would ...

kind regards,

Jos

---

So, basically, you're saying that a custom WindowListener, like the one Darryl suggested, would do the check just before calling the actual methods that closes the window - and therefore not checking whether it's actually closing or not?
I'm just checking if I understood it right (so a simple 'Yes' wouldn't be inappropriate).

Quote:

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Originally Posted by Muskar

So, basically, you're saying that a custom WindowListener, like the one Darryl suggested, would do the check just before calling the actual methods that closes the window - and therefore not checking whether it's actually closing or not?
I'm just checking if I understood it right (so a simple 'Yes' wouldn't be inappropriate).

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Yep, you understood right. One of those listeners (called later than yours) could bail out so the window won't be disposed.

kind regards,

Jos

Quote:

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One of those listeners (called later than yours) could bail out so the window won't be disposed.

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Not if the defaultCloseOperation is DISPOSE_ON_CLOSE (or even EXIT_ON_CLOSE). It's possible only if the window is set to DO_NOTHING_ON_CLOSE, and windowClosing(...) doesn't call dispose(). Any other listener in the chain cannot veto a dispose() invoked from windowClosing(...).

Quote:

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a custom WindowListener, like the one Darryl suggested, would do the check just before calling the actual methods that closes the window

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If the window is set to DISPOSE_ON_CLOSE, there is no other 'actual method that closes the window' and if it's DO_NOTHING_ON_CLOSE you have to invoke dispose() or if more appropriate, setVisible(false) from windowClosing(...).

db

Quote:

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Originally Posted by Darryl.Burke

If the window is set to DISPOSE_ON_CLOSE, there is no other 'actual method that closes the window' and if it's DO_NOTHING_ON_CLOSE you have to invoke dispose()

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I guess I'm sorry for my lack of knowledge of how exactly dispose() works.
With "actual methods", I was basically thinking of the methods that the dispose() method calls, within the method itself - I'd guess something that cleans up the frame for components or whatever, you get the point.
And that's why Jos' reply made sense to me.

Anyway, are you saying that windowClosing() dictates above all else in some way?
I'm sorry, I didn't quite get your clarification, if that was what it was.

EDIT:
I now have an additional question:
How do I do the same thing - but before "exiting" instead?
It seems that there's no method on the JFrame called .exit(), so I assume that I have to somehow reach the whatever-keeps-the-program-running or what?

I already tried the following:

Code:

---

        public void dispose() {
                System.out.println("I printed before closing!");
                super.dispose();
        }

---

and it wasn't called when I clicked on close (the frame is set to EXIT_ON_CLOSE)

Read the API for dispose() fo rbetter understanding.
Releases all of the native screen resources used by this Window, its subcomponents, and all of its owned children. That is, the resources for these Components will be destroyed, any memory they consume will be returned to the OS, and they will be marked as undisplayable.
When your frame is set to EXIT_ON_CLOSE there isn't any point in releasing resources, as the JVM is about to exit anyways. So don't expect dispose() to be invoked. And as I've been saying, overriding dispose() is NOT the correct approach to this requirement.

Code:

---

import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class FrameClosingListenerDemo {

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

      @Override
      public void run() {
        new FrameClosingListenerDemo().makeUI();
      }
    });
  }

  public void makeUI() {
    JFrame frame = new JFrame();
    frame.addWindowListener(new WindowAdapter() {

      @Override
      public void windowClosing(WindowEvent e) {
        System.out.println("Frame is closing");
      }
    });

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

---

db

Quote:

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Originally Posted by Darryl.Burke

When your frame is set to EXIT_ON_CLOSE there isn't any point in releasing resources, as the JVM is about to exit anyways. So don't expect dispose() to be invoked.

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So if I want to save data to a file, before Exiting, or open a dialog whether you want changes saved or not, I have no other option than using a windowListener() on all JFrames set to EXIT_ON_CLOSE, I presume?

Quote:

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Originally Posted by Darryl.Burke

And as I've been saying, overriding dispose() is NOT the correct approach to this requirement.

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I get how to make a windowListener - it's not that - but I still cannot see what makes overriding dispose() so terrible.
And with all due respect, you're only the 50% of the experts with that opinion, in this thread (and not to mention: I don't know random people's credibility of their respective opinion, unless they present proof).
And unless that changes dramatically - or you (or someone else) convince(s) me otherwise - I'm going to stick with my first solution, since it seemed convincing.

Quote:

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I have no other option than using a windowListener() on all JFrames set to EXIT_ON_CLOSE

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I don't see why any correctly designed application should have multiple JFrames set to EXIT_ON_CLOSE. But. If what you're looking for is a way to execute certain code on exit of your application, no matter how that exit is triggered -- which is not what you've been asking all along -- the correct way to do that is with a shutdown hook. Read the API for java.lang.Runtime#addShutdownHook(Thread).

Quote:

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I still cannot see what makes overriding dispose() so terrible.

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You've already discovered for yourself that dispose() isn't necessarily invoked when closing/hiding a window. But sure, wait for Jos to come back to this thread and comment on that. No probs.

db

Quote:

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Originally Posted by Darryl.Burke

But sure, wait for Jos to come back to this thread and comment on that. No probs.

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No further comments your honour; my suggestion was just a quick hack that only works if the dispose() method is called. My only artificial argument was that if (and only if) another WindowListener in the chain would bail out in an ugly way (by throwing an Exception) no dispose() and no further WindowListener(s) would be called at all ...

kind regards,

Jos

Quote:

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Originally Posted by Darryl.Burke

If what you're looking for is a way to execute certain code on exit of your application, no matter how that exit is triggered -- which is not what you've been asking all along -- the correct way to do that is with a shutdown hook. Read the API for java.lang.Runtime#addShutdownHook(Thread).

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It was merely a question out of curiosity (I have no intention on using several EXIT_ON_CLOSE JFrames) - and I must say, you provided exactly what I needed, thanks :)

Quote:

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Originally Posted by JosAH

My only artificial argument was that if (and only if) another WindowListener in the chain would bail out in an ugly way (by throwing an Exception) no dispose() and no further WindowListener(s) would be called at all ...

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And that would truly be exceptional, as far as I understand, so even though the difference is very small (and thanks to you both for providing both solutions), it seems like the optimal way to go.

Quote:

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Originally Posted by Muskar

And that would truly be exceptional, as far as I understand, so even though the difference is very small (and thanks to you both for providing both solutions), it seems like the optimal way to go.

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In general, when it comes to Swing, better listen to Darryl's advice (or Camick's advice, but I don't see him around anymore); I'm most certainly no Swing expert and for one reason or another I always lose track in it's documentation ;-)

kind regards,

Jos

Quote:

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Originally Posted by JosAH

In general, when it comes to Swing, better listen to Darryl's advice (or Camick's advice, but I don't see him around anymore); I'm most certainly no Swing expert and for one reason or another I always lose track in it's documentation ;-)

kind regards,

Jos

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Alright - but if you don't mind, I'll stick to your solution as long as no weird problems are occurring when disposing a window - but I'll keep it noted that I could change it to Darryl's extraordinarily advised way, if they should occur some day.