Objective-C Fundamentals

Categories
137
This code tells the compiler that you’re adding to the NSString an interface called
VowelDestroyer. This category adds a method called stringByDestroyingVowels
that takes no parameters and returns an NSString.
You implement the method in VowelDestroyer.m so that it can be called when
this method is called on an NSString object. Insert the following code into Vowel-
Destroyer.m.
Listing 6.10
VowelDestroyer.m
#import "VowelDestroyer.h"
@implementation NSString (VowelDestroyer)
- (NSString *)stringByDestroyingVowels {
NSMutableString *mutableString =
[NSMutableString stringWithString:self];
[mutableString replaceOccurrencesOfString:@"a"
withString:@""
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [mutableString length])];
[mutableString replaceOccurrencesOfString:@"e"
withString:@""
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [mutableString length])];
[mutableString replaceOccurrencesOfString:@"i"
withString:@""
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [mutableString length])];
[mutableString replaceOccurrencesOfString:@"o"
withString:@""
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [mutableString length])];
[mutableString replaceOccurrencesOfString:@"u"
withString:@""
options:NSCaseInsensitiveSearch
range:NSMakeRange(0, [mutableString length])];
b
Declare category
name
c
Create
NSMutableString
}
return [NSString stringWithString:mutableString];
@end
In this code, you declare the file to be an implementation of NSString again and
declare your category name once more B. Then you implement the method appropriately.
In this case you create a new type of string called an NSMutableString. If you
notice, NSStrings can’t be modified. NSString provides methods that modify a string
and return a whole new one, but NSMutableString can be used to modify an existing
string without having the modification methods return a whole new string. If this
method were to be used a lot in an application, this implementation would be the best
use of memory. After creating the NSMutableString c, you replace each vowel with
an empty string using the replaceOccurrencesOfString:withString:options:
range: method. Using the NSCaseInsensitive option with this method matches both