Re: in which thread shoud I use dialogs?

Lew <>
Wed, 23 Dec 2009 09:56:06 -0500
Marteno Rodia wrote:

An old Swing's rule says that all the UI operations should be carried
out in the event-dispatching thread, and other operations should be
done in other threads. I have written a GUI application which uses
multiple threads. Among them, there is a SwingWorker thread which can
inform user about an error, using a dialog for this purpose. Following
the aforementioned rule, I don't create the dialog in the SwingWorker
thread, but I put a new Runnable object in the Events' Queue.

In such context, I'm facing a great doubt: what if the dialog waited
for user's input? (some dialogs can do this, e.g. file chosers).
Wouldn't they blocked the event-dispatching thread?

No. Classes like JDialog are designed to work with other objects on the EDT.
  Modal dialogs block certain activities to the user, such as switching to a
different frame, but Swing does that by managing its own internal state. How
it ignores or eats the particular events can be a black box to us as
programmers. If we put our GUI on the EDT, Swing takes care of the rest.

Googling shows that this question is a FAQ. I didn't find in a quick search
whether Swing just handles modality in its main event loop or spawns a
hijacking thread. ISTR reading somewhere, somewhen that it's the latter.


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