Swing, awareness about unsaved data

Hi,

I am working on a Swing application for data maintenance (Java 6).
There is a JFrame with several JTextFields.
If the user is editing a record, there is UNSAVED data until she/he presses the Save-Button.

The application should always be aware if there is unsaved data. How can this be done?

Best regards
Gerald

Welcome to JavaRanch.

You could keep a boolean around that indicates whether there is unsaved data. Initially it would be false, but would be set to true in a key listener attached to each field.

(The logic in the key listener could be a bit more elaborate, like detecting if the new value is actually different from the last saved value. E.g., typing a key, and then hitting delete, should not count as a change in this context.)

Once the data is saved, the boolean is reset to false.

Thank you, Ulf!

A possible solution is: after each keystroke I compare the new
content of JTextField with the stored old string. If there is a difference
I set the "changed"-flag.

Does this make sense or is there a better way?

Best regards
Gerald

Well, if you really want to take the old, saved value into account, then you'd need a "changed" flag for each textfield. The overall "changed" status would then be the logical OR of all individual flags.

If you have just a single flag, then you can't take individual field's changed/unchanged status into account.

Consider these two cases: 1) field A changes, then field B changes, then A changes back to its original value, and 2) field A changes, then A changes back to its original value.
The warning "you have unsaved changes" (or whatever the code is going to do) should be shown for case 1, but not for case 2. But these cases can't be distinguished with just a single flag.

Thank you again!

I'll think it over.

But isn't there a standard solution to this (common) task?

Best regards
Gerald

this might be one way, flag is set on any keystroke - modify to suit.
e.g.
1)
type some text, click save, exit - exits without warning
2)
type some text, click save, ctrl-c to copy the text, exit - warning displays

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Testing
{
  boolean dirtyData = false;
  public void buildGUI()
  {
    final JFrame f = new JFrame();
    f.getContentPane().add(new JScrollPane(new JTextArea(10,20)));
    JMenuItem menu = new JMenuItem("Save");
    menu.addActionListener(new ActionListener(){
      public void actionPerformed(ActionEvent ae){
        save();
      }
    });
    JMenuBar menuBar = new JMenuBar();
    menuBar.add(menu);
    f.setJMenuBar(menuBar);
    f.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
    f.pack();
    f.setLocationRelativeTo(null);
    f.setVisible(true);
 
    KeyboardFocusManager.getCurrentKeyboardFocusManager()
     .addKeyEventDispatcher(new KeyEventDispatcher(){
        public boolean dispatchKeyEvent(KeyEvent ke){
          dirtyData = true;
          return false;
        }
    });
 
    f.addWindowListener(new WindowAdapter(){
      public void windowClosing(WindowEvent we){
        if(dirtyData)
        {
          int save = JOptionPane.showConfirmDialog(
            f.getContentPane(),"Data changed, save?","Save?",JOptionPane.YES_NO_OPTION);
          if(save == JOptionPane.YES_OPTION) save();
        }
        System.exit(0);
      }
    });
  }
  public void save()
  {
    //normal save code
    System.out.println("data saved");
    dirtyData = false;
  }
  public static void main(String[] args){new Testing().buildGUI();}
}

Hi Michael,

you've answered my next question:
How can I prevent data loss when closing the application?

Thanks a lot!
Gerald

This code won't work if user is changing state with a mouse.

> This code won't work if user is changing state with a mouse.

if you're talking about adding a mouseListener with right-click to open a popup
with 'paste' code, then, yes, it probably won't work.

also won't work if there's a tsunami or nuclear exlosion.

There are also controls that are usually used with a mouse. JSpinner, for example. So this code isn't very good choice for form-based frames and dialogs.

Anton Kuzmin wrote:There are also controls that are usually used with a mouse. JSpinner, for example. So this code isn't very good choice for form-based frames and dialogs.

The original post stated

Gerald Frischl wrote:There is a JFrame with several JTextFields.

The responses were geared to that statement. If you have a question about saving state involving a GUI with JSpinners, I suggest you start a new thread.

> There are also controls that are usually used with a mouse. JSpinner, for example....

no idea what you're on about, or why you'd even bother resurrecting a 5-year-old thread, but different components have different listeners.

in this thread textFields = keyListeners (as one option).

if the topic had been about spinners and the solution was about using changeListeners, would you have posted something like this?
"that's no good because it won't work with textfields"

I suspect you're just trolling a bit.

</end of discussion>