Little Message Dispatch, aka "Sending Primitives to the Main Thread"

Just ran across a Stack Overflow question on using primitives with performSelectorOnMainThread:. The original poster asks how he can send the message [myButton setEnabled:YES] from a background thread so it will execute on the main thread.

Alas, the obvious [myButton performSelectorOnMainThread:@selector(setEnabled:) withObject:(BOOL)YES waitUntilDone:YES]; is not only ugly, but also doesn't work. It used to kinda sorta work for scalar integer/pointer parameters that fit in a register, but it certainly wasn't a good idea and started breaking when Apple started to retain those parameters. Casting a BOOL to a pointer and back might work at times, sending it a retain will definitely not.

What to do? Well, I would suggest the following:

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[[myButton onMainThread] setEnabled:YES];

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Not only does it handle the primitives without a sweat, it is also succinct and readable. It is obviously implemented using Higher Order Messaging (now with Wikipedia page), and I actually have a number of these HOMs in MPWFoundation that cover the common use-cases:

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@interface NSObject(asyncMessaging)

-async;
-asyncPrio;
-asyncBackground;
-asyncOnMainThread;
-onMainThread;
-asyncOn:(dispatch_queue_t)queue;
-asyncOnOperationQueue:(NSOperationQueue*)aQueue;
-afterDelay:(NSTimeInterval)delay;


@end

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There is a little HOM_METHOD() Macro that generates both the trampoline method and the worker method, so the following code defines the -(void)onMainThread method that then uses performSelectorOnMainThread to send the NSInvocation to the main thread:

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HOM_METHOD(onMainThread)
        [invocation performSelectorOnMainThread:@selector(invokeWithTarget:) withObject:self waitUntilDone:YES];
}

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You can use MPWFoundation as is or take the above code and combine it with Simple HOM.