Re: Help! Swing & Threads
In article <PPmdnaftaqUszePZRVn-hg@comcast.com>,
Eric Sosman <esosman@acm-dot-org.invalid> wrote:
[ snip ]
JFileChooser doesn't block, or at any rate not for very
long (assuming the file system itself doesn't block for very
long). It reads some state (the contents of a directory) from
the file system, formats it for display, and returns -- at which
point the event-dispatching thread goes back to keeping the GUI
un-gluey. When the user twiddles one of the JFileChooser's
control doodads, the event-dispatching thread calls one of the
JFileChooser's event handlers; the JFileChooser responds by
scrolling the view or switching to a different directory or
whatever, updates its display accordingly, and once again returns
to the event-dispatching thread. The JFileChooser, like any good
GUI element, does not tie up the computer when there's nothing to
be done: It saves enough state to maintain awareness of what's
going on, returns to the event-dispatcher thread, and awaits
developments.
Well .... JFileChooser, as far as I can tell, isn't really itself
a GUI component, is it? The GUI components are the dialogs it pops
up, when showOpenDialog() or showSaveDialog() is called. And those
are modal dialogs, so they do indeed block any action on other GUI
components.
[ snip ]
Try this experiment: Write yourself a little GUI that fires
up *two* JFileChoosers simultaneously, and browse through a
couple different parts of your disk in side-by-side choosers.
The experiment itself won't teach you much, but pondering what's
going on might.
Below is my attempt to do -- well, something that's as close as
I can figure out to what you described. It doesn't behave as
you describe, though, since both the open dialogs are modal.
What am I doing differently from what you had in mind?
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;
public class JFC {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
final JFrame theFrame = new JFrame();
Container c = theFrame.getContentPane();
c.setLayout(new FlowLayout());
JButton b1 = new JButton("chooser 1");
c.add(b1);
b1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JFileChooser jfc = new JFileChooser();
int jfcReturn = jfc.showOpenDialog(theFrame);
if (jfcReturn == JFileChooser.APPROVE_OPTION) {
System.out.println("Chooser 1: you selected " +
jfc.getSelectedFile().getName());
}
}
});
JButton b2 = new JButton("chooser 2");
c.add(b2);
b2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
JFileChooser jfc = new JFileChooser();
int jfcReturn = jfc.showOpenDialog(theFrame);
if (jfcReturn == JFileChooser.APPROVE_OPTION) {
System.out.println("Chooser 2: you selected " +
jfc.getSelectedFile().getName());
}
}
});
theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
theFrame.pack();
theFrame.setVisible(true);
}
}
[ snip ]
--
B. L. Massingill
ObDisclaimer: I don't speak for my employers; they return the favor.