如果事件分配线程没有暂停，模态对话框如何等待？

Question

In an example below, the modal dialog is opened inside event dispatching thread. Since dialog is modal, method setVisible() is not return until it is closed.

One may suspect this is causing event dispatching thread paused, but it is wrong, since button is operating.

Hence, setVisible() method is not blocking the thread.

The question is: is it possible to show modal dialog without blocking a procedure?

package tests.javax.swing;

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class Try_JDialog_Modality2 {

    private static final Logger log = LoggerFactory.getLogger(Try_JDialog_Modality2.class);

    public static void main(String[] args) {

        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {

                AbstractAction popupAction = new AbstractAction("popup") {

                    @Override
                    public void actionPerformed(ActionEvent e) {
                        JOptionPane.showMessageDialog(null, "popup");
                    }

                };

                JDialog dialog = new JDialog((JFrame)null, true);
                dialog.setLayout(new FlowLayout());
                dialog.add(new JButton(popupAction));

                dialog.pack();
                dialog.setLocationRelativeTo(null);

                dialog.setVisible(true);

                log.debug("After set visible");



            }
        });


    }

}

UPDATE

I can do the same with the following snippet:

//dialog.setVisible(true);
            new Thread(new Runnable() {

                @Override
                public void run() {
                    dialog.setVisible(true);
                }
            }).start();

            log.debug("After set visible");

Is there a shorter way?

Answer 1

Your question:

The question is: is it possible to show modal dialog without blocking a procedure?

Yes, call the method before displaying the modal dialog. For certain things this might be best accomplished using a call-back type of set up, such as by using a PropertyChangeListener or other type of listener. If it is set up and called prior to visualizing the modal dialog, it should work.

As to the how portion of your question, I believe that it blocks input to the other windows but does not stop the Swing event thread. It does stop program flow from the calling code though, perhaps via a call to SwingUtilities.invokeAndWait(...) . Best for you to peek at the Swing source code for the details.

---

Edit Regarding your update, never do this:

new Thread(new Runnable() {

    @Override
    public void run() {
        dialog.setVisible(true);
    }
}).start();

as you are now guaranteeing to start the dialog off of the Swing event thread.

Answer 2

dialog.setVisible(true); shall be run on AWT Dispatcher thread. So you shall do it other way around.

public buttonPressed_OpenDialog_and_doTask(){
    new Thread(new Runnable() {
        @Override
        public void run() {
            /* my worker background task */
            dialog.dispose(); // at the end of task call this
        }
        }).start();
    dialog.setVisible(true);
    // we will continue when worker thread finishes
}

Note that even when you block on AWT event dispatcher thread (by method setVisible()). The AWT event dispatcher thread is still running somehow - so all AWT notifications are working like usual. See doc dialog.setVisible()

Note that all is ok even in case that background task would be to fast and it would call dialog.dispose() before dialog.setVisible(true) is called in previous thread. Luckily dialog.dispose() politely waits till dialog gets visible.