Re: Getting the value of GUI elements from non-main threads
Re: Getting the value of GUI elements from non-main threads
- Subject: Re: Getting the value of GUI elements from non-main threads
- From: Cem Karan <email@hidden>
- Date: Wed, 4 Feb 2009 16:39:26 -0500
On Feb 4, 2009, at 4:10 PM, Ken Thomases wrote:
On Feb 4, 2009, at 2:47 PM, Cem Karan wrote:
I know that we can only modify GUI elements from the main thread,
but can we get the values for objects from other than the main
thread? E.g., assume I have an editable NSTextField, and I have a
worker thread. The user edits the field, clicks a button, and the
main thread hands off the analysis to a worker thread. The worker
thread then directly queries the NSTextField via its stringValue
method. Is this kosher?
No. First, NSTextField isn't on the list of thread-safe classes.
OK, this is the part that I need to worry about, as I'm concerned
about crashes.
But quite aside from that, even if it were safe, you could not be
sure the value you would get is the value you should get. It might
have changed since the task was started.
In the scenario you describe, the button action method should
marshal all of the inputs for the worker unit that's to be processed
on the worker thread. Those inputs should be passed as integral
parts of the work unit to the worker thread.
Fully and wholeheartedly agreed; I should have spent more time
explaining. In my case, it doesn't even matter if the worker thread
gets the correct value, or a value at all, as this is some fast and
dirty test code that I'm going to use once and never look at again.
However, you're right, even for something like that (maybe especially
for something like that) its best to do it correctly. It just means I
need to rewrite my real code a little so that testing can go more
smoothly, something I was hoping to avoid doing.
Thanks,
Cem Karan
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