单击JButton时如何更新其外观？

Question

I'm working on a Java7 Swing "wizard" type of project that needs to validate a web address before continuing on to the next step of the wizard. The validation requires accessing a URL over the internet to verify that expected resources are available. In some cases, this can take a few seconds which can be long enough to confuse a user.

As a quick solution to this, I would like to disable the "next" button and change the display text while the validation is running so the user knows that the wizard is working and not hung up on anything. The problem is that when I add the code to modify the JButton, none of the changes happen until after the validation has completed. This is the case even if I change the button and call revalidate() before I execute the validation methods.

Here is an excerpt of what I've tried:

// create next button
next = new JButton("Next", new ImageIcon(getClass().getResource("/navigate_right.png")));

next.setActionCommand("MYACTION");
next.addActionListener(new ActionListener()
{
    @Override
    public void actionPerformed(ActionEvent e)
    {
        System.out.println("Is this the event dispatch thread? "
                + javax.swing.SwingUtilities.isEventDispatchThread());
        System.out.println("Changing button");

        next.setEnabled(false);
        next.setText("Testing Connection");
        next.getRootPane().revalidate();

        System.out.println("Validating Service");
        boolean isValidLocation = ServiceValidator.serviceExists(locationField.getText());

        // ...etc...

When I run this code, the lines "Changing button" and "Validating Service" both get printed before the actual button changes in the display. How can I get the JButton to change before System.out.println("Validating Service"); is printed?

Answer 1

The problem is that when I add the code to modify the JButton, none of the changes happen until after the validation has completed.

Your code is executing on the EDT, so you long running code prevents the GUI from repainting itself until the task is finished executing. You need to use a separate Thread for the long running task, maybe a SwingWorker . Read the section from the Swing tutorial on Concurrency for more information.