Question

I got problem with NSPredicate.

I got predicate:

NSPredicate* pr = [NSPredicate predicateWithFormat:@"FUNCTION('12.12345','round',3) = 12.123"];

and defined extension for NSString:

-(double) round:(NSNumber*) precision;

When I call manually:

NSLog(@"%f",[s round:3])

where s is NSString, it’s working prefectly, but used in NSPredicate rise:
NSInvalidArgumentException: rease -[NSCFString round]: unrecognized selector sent to instance.

I use solution used on page: http://funwithobjc.tumblr.com/post/2922267976/using-custom-functions-with-nsexpression

The main question is to make round function in NSPredicate, so any other solutions are welcome

Answer 1

The colon (:) must be part of the selector in the FUNCTION, so it should be FUNCTION('12.12345', 'round:', 3)

Also, I believe the round: method should return an NSNumber *, not a primitive type.