如何在Java Swing中侦听从其父JFrame关闭的JFrame窗口

Question

My program launches a JFrame from an already running parent JFrame. The second JFrame has autonomy from the first except for one condition - I require a button in the parent JFrame to be disabled when (and only when) the second JFrame is open to prevent additional JFrames being launched.

So my question is, how can I listen to the second JFrame's 'existence' from the parent JFrame in order to manipulate whether my button is active or not?

My parent JFrame launches the secondary JFrame as follows:

try { 
    second_frame Jframe = new second_frame(variable);
    Jframe.second_frame.setVisible(true);
    } catch (Exception e) {
                e.printStackTrace();
    }

followed by:

btn_open.setEnabled(false);

to disable the button once the second JFrame has been launched.

So how can I now listen to the second JFrame's window status from the first JFrame in order to re-enable the btn_open button.

Answer 1

One way is to add a WindowListener to the second frame. You can call button.setEnabled() every time the frame closes or opens. (There are implemented methods for that)

Here is an example:

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class Example {

    JButton button = new JButton("Open");

    public static void main(String args[]) {

        new Example();

    }

    public Example() {

        JFrame frame = new JFrame();

        button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {

                new secondFrame();

            }
        });

        frame.getContentPane().setLayout(new FlowLayout());
        frame.getContentPane().add(button);

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

    }

    class secondFrame extends JFrame implements WindowListener {

        public secondFrame() {

            setSize(200, 200);
            setVisible(true);

            addWindowListener(this);

        }

        @Override
        public void windowActivated(WindowEvent arg0) {

        }

        @Override
        public void windowClosed(WindowEvent arg0) {

        }

        @Override
        public void windowClosing(WindowEvent arg0) {

            button.setEnabled(true);

        }

        @Override
        public void windowDeactivated(WindowEvent arg0) {

        }

        @Override
        public void windowDeiconified(WindowEvent arg0) {

        }

        @Override
        public void windowIconified(WindowEvent arg0) {

        }

        @Override
        public void windowOpened(WindowEvent arg0) {

            button.setEnabled(false);

        }

    }

}