I'm using sample Apple code to use an "open file sheet" (rather
than an "open dialog") -- you know, the kind of dialog that
slides down from the top of a window like a window shade and is
attached to its parent window.
Anyway, the call to display the sheet does so, but doesn't
block. I want the caller to block like an ordinary dialog, yet
not have the event thread blocked so it can still process
repain events.
What I'm trying to do is push a new EventQueue, show the sheet,
wait(), pop the sheet, and continue. It works in the sense that
the event thread doesn't block, but what happens is quite often,
the entire program dies with a null pointer exception because
some of the events in the queue have null fields, i.e., it seems
like some events are bogus or corrupted somehow.
There are two event loops running in sync -- the Java/Swing
event loop, and AppKit's. When the sheet is up, it needs to
get events from the AppKit event loop (it might even push
its own). Are you calling show from the Java/Swing event
dispatch thread? Blocking the event dispatch thread waiting
for events on the AppKit thread may be problematic. If you
are calling from a different thread, I would expect this code
to work (without pushing a new event loop instance).
Note that sheets are fundamentally asynchronous (much like X11
callbacks). Since the sheet is window-modal, you should not
have any issues with components on the primary pane of the
window being active, the issue is just one of synchronizing
the calling code, and having it wait for the sheet to finish.
What is PoppableEventQueue? I Goggled it, but got no hits.
I think your problem is likely in the sync between the AppKit
and Java event queues, and that getting it right will require
inside knowledge of how Apple makes the event loop work. That
will require a DTS incident. For a quick and easy solution, I
suggest trying to call the sheet from a different thread, and
not messing around with creating a nested event loop. There is
serious voodoo going on between Swing and AppKit here.
There is also a timing issue when setting up an event loop in
Swing. I have seen calls to performSelectorOnMainThread (in
NSObject, called from Objective-C) sit waiting to execute until
a nested event loop finishes. A delay of a few hundred millis
to allow the nested event loop to stabilize before opening the
sheet might help. For more info on the timing issue, see:
