Re: How to change JPanels?
On Feb 11, 2:30 pm, markspace <nos...@nowhere.com> wrote:
On 2/11/2011 10:31 AM, Eric wrote:
<http://download.oracle.com/javase/tutorial/uiswing/concurrency/worker=
....>
What I've read so far from the Sun documentation suggests you have
that backwards, that all processing should be run off the EDT and the
SwingWorker should be used to run tasks on the EDT.
I think we're saying the same thing, just with slightly different words.
SwingWorker's doInBackground() method is run off the EDT. The
SwingWorker itself is normally created on and started from the EDT (via
execute()), but it doesn't have to be.
My confusion on that is the processing takes place within the
MenuItem's listener's actionPerformed method. Wouldn't that method
have to be on the EDT? I can't start a new thread to access the EDT
if I'm on the EDT can I?
Yes you can. Asynchronous is asynchronous. What you shouldn't do is
block the EDT while waiting for that thread to finish. You have exit
the EDT and let the asynchronous process finish on its own.
You can even call invokeLater() on the EDT. The Runnable is just queue=
d
up until you exit the EDT, then run at some point later.
Is there a way to tell it to finish the method I'm in which starts a
new thread to generate some new objects, and get back to the EDT to
update the screen to show the user the wait message, and know when
that process is done and get the new information loaded on the screen?
That's what SwingWorker does. Read the examples in that link I gave yo=
u
(the other ones on the following pages too).
So now my previous sample looks like this. I hope I'm doing this
right now. I'm not sure if it's the most efficient syntax but it
works.
import java.awt.CardLayout;
import java.awt.Container;
import java.awt.Menu;
import java.awt.MenuBar;
import java.awt.MenuItem;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;
import javax.swing.WindowConstants;
public class TestWindow {
InnerTestWindow win = null;
protected class InnerTestWindow extends JFrame {
protected CardLayout cardLayout = null;
protected Container contentPane = null;
protected JPanel panelOne = null;
protected JPanel panelTwo = null;
private JTextArea dummyTextOne = null;
private JTextArea dummyTextTwo = null;
protected InnerTestWindow() {
contentPane = getContentPane();
contentPane.setLayout(new CardLayout());
cardLayout = (CardLayout)contentPane.getLayout();
MenuBar menuBar = new MenuBar();
Menu menu = new Menu("Test");
addMenuItem(menu,"First","FirstItem",new
FirstItemListener());
menuBar.add(menu);
setMenuBar(menuBar);
setDefaultCloseOperation( WindowConstants.DISPOSE_ON_CLOSE );
setSize(600, 600);
setLocation(100, 100);
panelOne = new JPanel();
contentPane.add(panelOne,"Panel One");
dummyTextOne = new JTextArea("Panel One");
panelOne.add(dummyTextOne);
panelTwo = new JPanel();
contentPane.add(panelTwo,"Panel Two");
dummyTextTwo = new JTextArea("Panel Two");
panelTwo.add(dummyTextTwo);
setContentPane(contentPane);
loadOne();
}
private void addMenuItem(Menu menu, String menuItemTitle,
String menuItemName, ActionListener menuListener) {
MenuItem menuItem = new MenuItem(menuItemTitle);
menuItem.setActionCommand(menuItemName);
menuItem.addActionListener(menuListener);
menu.add(menuItem);
}
protected class FirstItemWorker extends SwingWorker {
BufferedImage[] renderedPngPages = null;
int waitTime;
protected FirstItemWorker(int waitTimeIn) {
waitTime = waitTimeIn;
}
protected Integer doInBackground() {
long t0, t1;
t0 = System.currentTimeMillis();
do {
t1 = System.currentTimeMillis();
} while ((t1 - t0) < (waitTime));
return 0;
}
protected void done() {
if (isCancelled()) {
return;
}
loadOne();
}
}
private class FirstItemListener implements ActionListener {
public void actionPerformed(ActionEvent ev) {
loadTwo();
FirstItemWorker fiw = new FirstItemWorker(3000);
fiw.execute();
}
}
protected void loadOne() {
cardLayout.show(contentPane, "Panel One");
repaint();
}
public void loadTwo() {
cardLayout.show(contentPane, "Panel Two");
repaint();
}
}
public void createWindow() {
win = new InnerTestWindow();
win.setVisible(true);
}
public static void main(String[] args) throws Exception {
TestWindow testWin = new TestWindow();
testWin.createWindow();
}
}