how can i do showMessageDialog when i click exit on a JFrame

Question

i developed a simple image editor in java, how can i do to show a message dialog when i click exit on a JFrame to ask the user if he want to save the work?

thank's everybody

Answer 1

Use a JOptionPane showing up on a specific event. For example the window closing event in the WindowListener.

WindowListener wl = new WindowAdapter() {
     public void windowClosing(WindowEvent e) {
          // add the option pane code here
     }
};
JFrame yourFrame = // your frame here
yourFrame.addWindowListener(wl);

A JOptionPane can be created as such:

final JOptionPane optionPane = new JOptionPane(
    "The only way to close this dialog is by\n"
    + "pressing one of the following buttons.\n"
    + "Do you understand?",
    JOptionPane.QUESTION_MESSAGE,
    JOptionPane.YES_NO_OPTION);

Resulting option pane. Another alternative is to use one of the more specialized factory methods.

int option = JOptionPane.showConfirmDialog(null,"Exit Application?");
if(option == JOptionPane.YES_OPTION) {
    System.exit(0);
}

When you add a new close handler like this i would suggest to deactivate the default handler using this code:

yourFrame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);

For more information about the setDefaultCloseOperation consult the documentation.

Hope this helps

Answer 2

Check out Closing an Application for basic information and examples.

You need to follow two basic steps:

1. Add a WindowListener to the frame and handle the windowClosing(...) event
2. Use the setDefaultCloseOperation(...) on the frame to allow the WindowListener to take control of the closing event.

The above link shows a simple example as well as a simple API that does both of the above steps so all you need to do is create an Action to handle your closing logic.