JoptionPane ShowConfirmDialog

问题

I have a Java program. When I run the program, it will give me a GUI which as I attached.

When I want to close it, it will prompt out a confirm dialog. If I press the Yes button, it will quit the program using System.exit().

public static void main(String args[])
{
    ButtonTest app = new ButtonTest( );
    app.addWindowListener( 
        new WindowAdapter( )
        {
            public void windowClosing (WindowEvent e)
            {
                String message = " Really Quit ? ";
                String title = "Quit";
                int reply = JOptionPane.showConfirmDialog(null, message, title, JOptionPane.YES_NO_OPTION);
                if (reply == JOptionPane.YES_OPTION)
                {
                    System.exit(0);
                }

            }
        }
    );
}

If I don't want to quit the program, what can I do? System.continued() ?

回答1:

You Don't need the else in this case

回答2:

Try setting this,

app.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE)

[Edited]

So, your code will become something like this,

public static void main(String args[]) {
    ButtonTest app = new ButtonTest();
    app.addWindowListener(new WindowAdapter() {
        public void windowClosing(WindowEvent e) {
            int reply = JOptionPane.showConfirmDialog(null,
                    "Really Quit ?", "Quit", JOptionPane.YES_NO_OPTION);
            if (reply == JOptionPane.YES_OPTION)
                System.exit(0);
        }
    });
    app.setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE);
    app.setSize(640, 480);
    app.setVisible(true);
}

[Explanation]

You might be thinking that why it is like that. The behaviour of windows close button for JFrame, unlike Frame,is to hide the window. Therefore, it will hide/close the window anyway. But when you specify that it must also exit the program, when the user click yes. Then, besides closing the window, it also exits the program. And when user clicks no, it does nothing but closes the window anyway. Hence, you must tell it explicitly that DO_NOTHING_ON_CLOSE.

[Docs]

Unlike a Frame, a JFrame has some notion of how to respond when the user attempts to close the window. The default behavior is to simply hide the JFrame when the user closes the window. To change the default behavior, you invoke the method setDefaultCloseOperation(int). To make the JFrame behave the same as a Frame instance, use setDefaultCloseOperation(WindowConstants.DO_NOTHING_ON_CLOSE).

Ref: JFrame docs

回答3:

If you will ask me, I will go with, on YES SELECTION instead of abruptly closing my Application with System.exit(0), I will choose the gracious way of closing my Application, by using frameObject.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE) and on NO SELECTION , I will go for frameObject.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE). Here is one sample program for your help :

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class ApplicationCloseExample
{   
    private void displayGUI()
    {
        final JFrame frame = new JFrame("Application Close Example");

        frame.addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent we)
            {
                int result = JOptionPane.showConfirmDialog(
                                frame, "Do you want to Exit ?"
                                , "Exit Confirmation : ", JOptionPane.YES_NO_OPTION);
                if (result == JOptionPane.YES_OPTION)               
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                else if (result == JOptionPane.NO_OPTION)   
                    frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
            }
        });

        frame.setSize(300, 300);
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new ApplicationCloseExample().displayGUI();
            }
        });
    }
}

回答4:

If you want the program to continue when you press NO, place the rest of your code in else block or call the function where you have placed the rest of your code.

Removing else block is also an option if you don't want to place any action on the NO button because the JOptionPane.showConfirmDialog() will close anyways. You can continue with rest of your code after the if statement.

FYI- There is no System.continue(). The program pretty much does that on it's own.

回答5:

You can add an else block. if you want to run the main method again (which I assume you do) it should look like this. You should have some method which you run if the user chooses no, whether it is the main method main(null) or another method.

public static void main(String args[])
{
ButtonTest app = new ButtonTest( );
app.addWindowListener( 
        new WindowAdapter( )
        {
            public void windowClosing (WindowEvent e)
            {
                String message = " Really Quit ? ";
                String title = "Quit";
                int reply = JOptionPane.showConfirmDialog(null, message, title, JOptionPane.YES_NO_OPTION);
                if (reply == JOptionPane.YES_OPTION)
                {
                    System.exit(0);
                } 
                else 
                {
                  //whatever you plan on running instead here, instead of quitting,
                  //main(null) to run the main method, or put another method if you want
                }
            }
        }
    );
}

来源：https://stackoverflow.com/questions/10716828/joptionpane-showconfirmdialog

标签

java

swing

if-statement

conditional

joptionpane