How do you use NSRegularExpression's replacementStringForResult:inString:offset:template:

Question

I have a series of characters that I want to match with a regular expression, and replace them with specific strings depending on what they are.

Example:

In

Answer 1

I needed a more generic solution for the same problem so I refined Dano's answer to a method like this, with a sample usage explained below:

- (NSMutableString *)replaceSubstringsInString:(NSString*)string
                                    usingRegex:(NSString*)searchRegex
                              withReplacements:(NSDictionary*)replacements {

    NSMutableString *newString = [string mutableCopy];
    __block NSInteger offset = 0;

    NSError *error = NULL;

    NSRegularExpression *regex = [NSRegularExpression
                                  regularExpressionWithPattern:searchRegex
                                  options:0
                                  error:&error];

    [regex enumerateMatchesInString:string
                            options:0
                              range:NSMakeRange(0, [string length])
                         usingBlock:^(NSTextCheckingResult *match, NSMatchingFlags flags, BOOL *stop){

                             NSRange resultRange = [match range];
                             resultRange.location += offset;

                             NSString *substring = [string substringWithRange:match.range];

                             __block NSString* replacement;

                             [replacements enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {

                                 if ([key isEqualToString:substring]) {
                                     replacement = obj;
                                 }

                             }];

                             [newString replaceCharactersInRange:resultRange withString:replacement];

                             offset += ([replacement length] - resultRange.length);
                         }];

    return newString;
}

Usage:

NSString *string = @"This is the input string where i want to replace 1 2 & 3";
NSString *searchRegex = @"\\b[1-3]\\b";
NSDictionary *replacements = @{@"1":@"ONE",@"2":@"TWO",@"3":@"THREE"};

NSMutableString *result = [self replaceSubstringsInString:string
                                               usingRegex:searchRegex
                                         withReplacements:replacements];

Explanation: You just have to pass in the string to search for the matching substrings, along with the desired regexSearch pattern and a replacements dictionary containing the string pairs with the key being the substring to be replaced and the object with the desired replacement string.

Output:

 //   This is the input string where i want to replace ONE TWO & THREE