Kelvin Chung wrote:
I'm trying to find a good way of associating an Objective-C object
with an arbitrary Java object, so that you could essentially
delegate the Objective-C method call to a Java object. I envision
that this would have to be done using JNI. However, I don't know
the specifics of how it can be done.
How much do you know about JNI? If it's not much, then that's your
first task: learn JNI. There are jobject references, method ids,
threading invocation requirements, and so on, and you will end up
having to know about all of them.
If you don't have a copy of the JNI Specification and Programmer's
Guide, you will definitely need that. It doesn't matter what other
books you have, the spec is the definitive reference.
http://java.sun.com/docs/books/jni/
Once you have some experience with JNI, the key thing you need to
know is that you must make a global-ref for every jobject that needs
to survive between calls to the JVM. You might think of the global-
ref as the equivalent of retain, although that's not a precise
analogy, and like many analogies, taking it too literally leads to
grief. It's closer to a strong reference in GC'ed Obj-C, but that's
not an exact analogy either.
I wish you luck on this. Although what you ask for may seem simple
or straightforward, it is a considerable undertaking, and I don't
think you realize how considerable it is.
And yes, I saw your post entitled "Developing with Cocoa" on java-dev
(and the replies), and I think there's a lot more complexity there
than what you perceive. In particular, re your reply here:
http://lists.apple.com/archives/java-dev/2009/May/msg00004.html
"It seems that using a Cocoa frontend is easier."
Some things seem simple because they are. Other things seem simple
only because we're ignorant of how complex they really are. All that
happens is you trade one bucket of hurt for a different and
frequently larger bucket of hurt. In my opinion, this is one of the
latter.
If you prove me wrong, however, please post a follow-up to the list,
because I have a use for such a thing, if it works reliably and
smoothly.
-- GG
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