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Re: performSelectorOnMainThread
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Re: performSelectorOnMainThread


  • Subject: Re: performSelectorOnMainThread
  • From: glenn andreas <email@hidden>
  • Date: Sat, 10 Jan 2009 13:12:45 -0600


On Jan 10, 2009, at 1:00 PM, John Love wrote:

-performSelectorOnMainThread:withObject:waitUntilDone:, according to Apple docs, is passed a SEL method that "should not have a significant return value".

I wish it to return a INT and I figure that that qualifies as in- significant. Given that assumption, my real question is how to implement it. I call:

[self performSelectorOnMainThread:@selector:mySimpleSelector withObject:nil waitUntilDone:YES];

(int) mySimpleSelector {
	if (whatever) return 0;
	else          return 1;
}

via my call to -performSelectorOnMainThread, just how do I access - mySimpleSelector's returned INT? The simplest answer is to not have a return value at all, but rather store the INTs in a global; but I figure there is no time like the present to learn to solve this problem the right way.


The most general solution is to make an NSInvocation (a bit of a pain the first dozen times you do it), and then have that invocation performSelectorOnMainThread, with the @selector(invoke). Afterwards, you can extract the return value from the invocation. This also gives you the advantage of being able to call things with a much wider range of number of parameters and parameter types (e.g., passing an NSRect).


(If waitUntilDone: NO is used, it's a bit trickier to figure out when the thing is done - you'd probably want to use a semaphore - which is one of the reasons that, in general, you shouldn't have a return value).


Glenn Andreas email@hidden <http://www.gandreas.com/> wicked fun! JSXObjC | the easy way to unite JavaScript and Objective C




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References: 
 >performSelectorOnMainThread (From: John Love <email@hidden>)

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