How to set the JFrame as a parent to the JDialog

问题:

I am having trouble to set the frame as a owner to the dialog. Normally when I extend JDialog class for creating a dialog then I use super(frame) to specify the owner of the dialog such that both of them are not disjoint when you press alt+tab. But when I create a dialog using new like JDialog dialog = new JDialog() then I am unable to specify the frame as owner to the dialog.

Following example demonstrates above two approaches. Top Click button opens a dialog which is without extending JDialog. Bottom Click button opens a dialog with extending JDialog.

import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

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

public class DialogEx {

    public static void main(String[] args) {
        Runnable r = new Runnable() {
            public void run() {
                new DialogEx().createUI();
            }
        };
        EventQueue.invokeLater(r);
    }   

    private void createUI() {
        final JFrame frame = new JFrame();
        frame.setLayout(new BorderLayout());

        JButton button1 = new JButton("Top Click");
        JButton button2 = new JButton("Bottom Click");

        button2.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                new DialogExtend(frame).createUI();
            }
        });

        button1.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                new DialogWithoutExtend(frame).cretaUI();
            }
        });

        frame.setTitle("Test Dialog Instances.");
        frame.add(button1, BorderLayout.NORTH);
        frame.add(button2, BorderLayout.SOUTH);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(300, 200));
        frame.setVisible(true);
    }

    class DialogExtend extends JDialog {
        private JFrame frame;
        public DialogExtend(JFrame frame) {
            super(frame);
            this.frame = frame;
        }

        public void createUI() {
            setLocationRelativeTo(frame);
            setTitle("Dialog created by extending JDialog class.");
            setSize(new Dimension(400, 100));
            setModal(true);
            setVisible(true);
        }
    }

    class DialogWithoutExtend {

        private JFrame frame;
        public DialogWithoutExtend(JFrame frame) {
            this.frame = frame;
        }

        public void cretaUI() {
            JDialog dialog = new JDialog();
            dialog.setTitle("Dialog created without extending JDialog class.");
            dialog.setSize(new Dimension(400, 100));
            dialog.setLocationRelativeTo(frame);
            dialog.setModal(true);
            dialog.setVisible(true);
        }
    }
}

回答1:

A dialog's (or window's) owner can be set only in the constructor, so the only way to set it is by using a constructor which takes the owner as parameter, like:

class DialogWithoutExtend {

    private JFrame frame;
    public DialogWithoutExtend(JFrame frame) {
        this.frame = frame;
    }

    public void cretaUI() {
        JDialog dialog = new JDialog(frame);
        dialog.setTitle("Dialog created without extending JDialog class.");
        dialog.setSize(new Dimension(400, 100));
        dialog.setLocationRelativeTo(frame);
        dialog.setModal(true);
        dialog.setVisible(true);
    }
}