Categories in Objective C not working

Question

I have a similar problem to the link below.

Categories in Objective-C aren't working

I'm a newbie to Objective C, so please excuse the ignorance. I need to support themes in my project, and I found this interesting solution (https://github.com/tombenner/nui) that I am trying to integrate into my solution. I have integrated the project as explained in the installation instructions on the nui page. This software is dependent on CoreParse which needs to be added as a sub-project to you app. I have done this.

The folder structure is as follows:

--CODE
   --CoreParse
   --MyApp
       -ExternalProjects

I dragged the Coreparse project file into the ExternalProject Subfolder in my project.

When I run the project, I kept getting messages like "unrecognized selector sent to instance 0x81b42e0" which I fixed by simply combining ALL the category code into the parent class.

Now I am encountering the same error again, only this time it is in a category extension of the NSSet class in the Apple libraries, so my combining workaround will not suffice.

The error I get is:

2014-03-26 11:16:16.358 MomApp[1409:c07] -[__NSSetM cp_map:]: unrecognized selector sent to instance 0x81b0210

When I do a "po" on my error, I get the following:

po 0x81b0210 $0 = 139762688 {( (null) ::= • )}

Edit: The code calling this comes from a packege I downloaded on github (CoreParse)

    while ([processingQueue count] > 0)
{
    NSSet *kernel = [processingQueue objectAtIndex:0];
    NSSet *itemSet = [self lr0Closure:kernel];
    //The next line causes the error
    NSSet *validNexts = [itemSet cp_map:^ id (CPItem *item) {return [item nextSymbol];}];

    for (CPGrammarSymbol *s in validNexts)
    {
        NSSet *g = [self lr0GotoKernelWithItems:itemSet symbol:s];
        if (![c containsObject:g])
        {
            [processingQueue addObject:g];
            [c addObject:g];
        }
    }

    [processingQueue removeObjectAtIndex:0];
}

The .h and .m files where this extension resides are shown below: .h File

//
//  NSSetFunctional.h
//  CoreParse
//
//  Created by Tom Davie on 06/03/2011.
//  Copyright 2011 In The Beginning... All rights reserved.
//

#import <Foundation/Foundation.h>


@interface NSSet(Functional)

- (NSSet *)cp_map:(id(^)(id obj))block;

@end

.m File

//
//  NSSetFunctional.m
//  CoreParse
//
//  Created by Tom Davie on 06/03/2011.
//  Copyright 2011 In The Beginning... All rights reserved.
//

#import "NSSetFunctional.h"
#import <Foundation/Foundation.h>


@implementation NSSet(Functional)

- (NSSet *)cp_map:(id(^)(id obj))block
{
    NSUInteger c = [self count];
    id *resultingObjects = malloc(c * sizeof(id));

    NSUInteger nonNilCount = 0;
    for (id obj in self)
    {
        id r = block(obj);
        if (nil != r)
        {
            resultingObjects[nonNilCount] = r;
            nonNilCount++;
        }
    }

    NSSet *s = [NSSet setWithObjects:resultingObjects count:nonNilCount];
    free(resultingObjects);
    return s;
}

@end

I am at a loss as to how to get this to work. As I said, I am a newbie to IOS programming and this truly has me stumped. Any help would be greatly appreciated.

Answer 1

Make sure the category's implementation file (NSSetFunctional.m) is being compiled and linked into your target. There are a couple ways to verify this, but the easy way is to select that file in Xcode, open the Utilities drawer (right 'sidebar'), and select the File inspector (page icon). Under "Target Membership" make sure the box next to your app's target is checked.

If this option is not checked, the implementation for those category methods won't be included in the compiled binary, and you'll get exactly the error you describe.