Ignore UIButton's touch event in a long task time

Ignore UIButton's touch event in a long task time

I want ignore all touch event of a button while a long task is running.
- (void)buttonAction{
NSLog(@"click!");
button.enabled = NO;
[self longTask];
}
- (void)longTask{
NSLog(@"task begin!");
sleep(5);
NSLog(@"task finished!");
button.enabled = YES;
}
During the longTask time, I click the button again, it really nothing
happens. BUT, when the longTask is finished, it automatically respond to
the click events and execute the longTask again! How many times I clicked
when the button's enabled value is 'NO', the longTask will perform how
many times.
2013-08-20 09:24:49.478 AppName[2518:c07] click!
2013-08-20 09:24:49.479 AppName[2518:c07] task begin!
2013-08-20 09:24:54.481 AppName[2518:c07] task finished!
2013-08-20 09:24:54.482 AppName[2518:c07] click!
2013-08-20 09:24:54.482 AppName[2518:c07] task begin!
2013-08-20 09:24:59.484 AppName[2518:c07] task finished!
I tried to set serInteractionEnabled and got the same result.
How can make it ignore all touch event when a long task is running and
never performs the task? In other words, only executes the longTask when
the button's clicked at it's enabled value is 'YES'?
Thanks any help!