Objective-C Categories: Method not called - objective-c

Question

I'm trying to learn the basics of Objective-C through reading "Learning Objective-C 2.0" Theres an exercise on categories where your asked to add a method to NSString through use of categories. My simple program is below. it (should) take a string and then reverses the order of the words.
Main
#import <Foundation/Foundation.h>
#import "CatNSString.h"
int main(int argc, const char * argv[]) {
#autoreleasepool {
NSString *test = #"Dog bites Man";
NSString *test1 = nil;
test1 = [test1 reverseWords: test];
NSLog(#"%# : %#", test, test1);
}
return 0;
}
Interface
#import <Foundation/Foundation.h>
#interface NSString (CatNSString)
- (NSString*) reverseWords:(NSString*)string;
#end
Implementation
#import "CatNSString.h"
#implementation NSString (CatNSString)
- (NSString*) reverseWords: (NSString*) string
{
NSString *stringReturn = nil;
NSArray *arrayString = [string componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
stringReturn = [string stringByAppendingString:#"hello"];
for (NSString *word in arrayString)
{
NSString *stringTmp1 = word;
NSString *stringTmp2 = stringReturn;
stringReturn = [stringTmp1 stringByAppendingString:stringTmp2];
NSLog(#"stringTmp1: %#", stringTmp1);
}
return stringReturn;
}
#end
It compiles but the program acts as though the method is never called. If I place a NSLog call in the method there is no output to the console. Can anyone see what I'm not doing that I should be doing?

Answer 1

You just did it wrong way.
Here is the proper way to define a Category:
#interface NSString (CatNSString)
-(NSString *)reverse;
#end
#implementation NSString (CatNSString)
-(NSString*)reverse {
// `Self` keyword will refer to your original string, no need to pass it as a parameter
NSArray *words = [self componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
return [[[words reverseObjectEnumerator] allObjects] componentsJoinedByString:#" "];
}
#end
And in your main code, do the following:
NSString *test = #"Dog bites Man";
NSLog(#"%#", [test reverse]);