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open a JFileChooser/ modal window will block the event dispatching thread

Posted on 2009-07-10
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Last Modified: 2013-11-23
Please tell me whether opening a JFileChooser/ modal window in event handling code will block the event dispatching thread.

Thank you
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Question by:pdidominic
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Expert Comment

by:CEHJ
ID: 24822310
Yes it will. Use a SwingWorker
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objects earned 500 total points
ID: 24822332
no it won't
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Expert Comment

by:objects
ID: 24822347
If it did then opening JFileChooser would freeze up your gui
you'll find example and discussion here
http://java.sun.com/docs/books/tutorial/uiswing/components/filechooser.html
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Expert Comment

by:CEHJ
ID: 24822528
>>If it did then opening JFileChooser would freeze up your gui

(which is exactly what it does do)

All you need to do to demonstrate this is to try to close your main window with the file chooser dialog open
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Author Comment

by:pdidominic
ID: 24823366
i have a little confuse here. Despite the JFileChooser dialog blocks the actionPerform event handling code as the following snippet but the event dispatching thread is still executed :-??

public class FileChooser extends JFrame
{
	public FileChooser()
	{
		initComponents();
		Runnable runner = new Runnable()
		{
			public void run()
			{
				ActionListener actionListener = new ActionListener()
				{
					public void actionPerformed(ActionEvent actionEvent)
					{
						testTxt.setText(testTxt.getText() + 'a');
						System.out.println(SwingUtilities.isEventDispatchThread());
					}
				};
				Timer timer = new Timer(500, actionListener);
				timer.start();
			}
		};
		EventQueue.invokeLater(runner);
	}
 
	public static void main(String[] args)
	{
		
		new FileChooser().setVisible(true);
		
	}
 
	private void startBtnActionPerformed(ActionEvent e)
	{
		JFileChooser fileChoose = new JFileChooser();
		
		System.out.println(SwingUtilities.isEventDispatchThread() + "---------");
		fileChoose.showOpenDialog(FileChooser.this);
		System.out.println(SwingUtilities.isEventDispatchThread() + "---------");
	}

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Expert Comment

by:ksivananth
ID: 24823386
>>All you need to do to demonstrate this is to try to close your main window with the file chooser dialog open

I think, object is right, it will block UI( parent ) but not the event dispatching thread! if the event dispatching thread blocked, you will not see the drawing in the back UI, all will be greyed out!
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Author Comment

by:pdidominic
ID: 24823393
in this snippet, i have a simple form with a textarea and a button. Pressing the button will open a file chooser dialog. I also have a Timer that constantly updates the textarea.
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by:CEHJ
ID: 24824228
>>it will block UI( parent )

UIs don't get blocked - only threads get blocked ;-)
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by:CEHJ
ID: 24824285
http://en.wikipedia.org/wiki/Modal_window

Look at the first sentence under criticisms (which to me is absurd - if you don't want it to block workflow then don't make it modal)
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Expert Comment

by:objects
ID: 24828305
> but the event dispatching thread is still executed :-??

thats because the event dispatch thread does *not* get blocked as I stated above.
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Expert Comment

by:objects
ID: 24828378
> in this snippet, i have a simple form with a textarea and a button. Pressing the button will open a
> file chooser dialog. I also have a Timer that constantly updates the textarea.

And does it continue to update?  That should verify whether it is blocked or not.
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Expert Comment

by:objects
ID: 24836892
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