Question

I created UILabel category which would do extra work when font property is changed.

I have chosen category over sublassing so I do not have to change class for all labels in my all XIB files. I just add this category declaration to the prefix header and category is visible in the whole project scope.

Implementation file:

//
//  UILabel+XIBCustomFonts.m


#import "UILabel+XIBCustomFonts.h"

@implementation UILabel (XIBCustomFonts)
BOOL comes_from_nib = NO;


-(id)initWithCoder:(NSCoder *)aDecoder_{

    self = [super initWithCoder:aDecoder_];

    if (self) {
        comes_from_nib = YES;

    }
    return self;
}

-(void)setFont:(UIFont *)font_{

    [super setFont:font_];
    NSLog(@"Setting from for label from XIB for name:%@ size: %.1f - do font theme replacement if needed", self.font.fontName, self.font.pointSize);

}
@end

The surprising thing is the crash with following log:

-[UIButtonLabel setFont:]: unrecognized selector sent to instance 0x9ad1b70
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIButtonLabel setFont:]: unrecognized selector sent to instance 0x9ad1b70'

Where did UIButtonLabel came form?

It happens even if I do extra Class checking in setFont: setter:

if ([self class] != [UILabel class] || !comes_from_nib) {

        [super setFont:font_];
        return;

    }

Is there any way to override setFont: setter in UILabel without subclassing?

Answer 1

You cannot call super methods in categories! Never!
This is not possible when you use a category to augment a class’ functionality, you are not extending the class, you are actually wholly overriding the existing method, you lose the original method completely. That’s why your error appears.