Highlight particular characters in the string for all the characters of given string

Question

Particular characters are to be highlighted in red color on the label so I wrote below function which works well, but I want to confirm, is there any other efficient way of doing this ? e.g.

-(NSMutableAttributedString*)getAttributeText:(NSString*)string forSubstring:(NSString*)searchstring {
    NSMutableAttributedString *text = [[NSMutableAttributedString alloc] initWithString:_lblName.text];
    NSRange searchRange = NSMakeRange(0,string.length);
    for (NSInteger charIdx=0; charIdx<searchstring.length; charIdx++){
        NSString *substring = [searchstring substringWithRange:NSMakeRange(charIdx, 1)];
        NSRange foundRange;
        searchRange.location = 0;
        while (searchRange.location < string.length) {
            searchRange.length = string.length-searchRange.location;
            foundRange = [string rangeOfString:substring options:1 range:searchRange];
            [text addAttribute: NSForegroundColorAttributeName value: [UIColor redColor] range:foundRange];
            if (foundRange.location != NSNotFound) {
                searchRange.location = foundRange.location+foundRange.length;
            } else {
                // no more substring to find
                break;
            }
        }
    }
    return text;
}

Below is the code how I use it, and result as well

NSString *string = @"James Bond Always Rocks";
_lblName.text = string;
_lblAttributedName.attributedText = [self getAttributeText:string forSubstring:@"ao"];

Update

NSString *string = @"James Bond Always Rocks";    
NSRange range = [string rangeOfCharacterFromSet:[NSCharacterSet characterSetWithCharactersInString:@"J"] options:NSCaseInsensitiveSearch];
NSLog(@"range->%@",NSStringFromRange(range)); //This prints range->{0, 1}

NSString *string = @"James Bond Always Rocks";    
NSRange range = [string rangeOfCharacterFromSet:[NSCharacterSet characterSetWithCharactersInString:@"j"] options:NSCaseInsensitiveSearch];
NSLog(@"range->%@",NSStringFromRange(range)); //This prints range->{2147483647, 0}

Answer 1

You can simplify it by searching for a pattern ("[ao]+" in your example) to eliminate the outer loop:

NSString *string = @"James Bond Always Rocks";
NSString *searchstring = @"ao";
NSMutableAttributedString *text = [[NSMutableAttributedString alloc] initWithString:string];

// A regular expression pattern that matches a sequence of the characters in "searchString":
NSString *pattern = [NSString stringWithFormat:@"[%@]+", [NSRegularExpression escapedPatternForString:searchstring]];

NSRange foundRange = [string rangeOfString:pattern options:NSRegularExpressionSearch|NSCaseInsensitiveSearch];
while (foundRange.location != NSNotFound) {
    [text addAttribute: NSForegroundColorAttributeName value: [UIColor redColor] range:foundRange];
    NSRange nextRange = NSMakeRange(foundRange.location + foundRange.length, string.length - foundRange.location - foundRange.length);
    foundRange = [string rangeOfString:pattern options:NSRegularExpressionSearch|NSCaseInsensitiveSearch range:nextRange];
}

Answer 2

Here is my version, this is very basic approach using simple loops.

Why I posted it because I tracked the efficiency and please see the time taken by each of the implementations.

2014-03-14 15:48:42.792 TimeEfficiency[1166:303] My: 0.000073 seconds

2014-03-14 15:48:45.319 TimeEfficiency[1166:303] martin: 0.000278 seconds

2014-03-14 15:48:48.263 TimeEfficiency[1166:303] avt: 0.000029 seconds

2014-03-14 15:48:51.152 TimeEfficiency[1166:303] janak: 0.000092 seconds

Hence Avt's is best in time-performance.

---

NSString *string = @"James Bond Always Rocks";
NSString *searchstring = @"ao";

NSMutableArray *characters = [NSMutableArray new];
for (NSInteger i=0; i<searchstring.length; i++) {
    [characters addObject:[searchstring substringWithRange:NSMakeRange(i, 1)]]; //ao
}
//store all the location of each of the char
NSMutableArray *locations = [NSMutableArray new];
for (NSInteger i=0; i<string.length; i++) {
    if ([characters containsObject: [string substringWithRange:NSMakeRange(i, 1)]] ){
        [locations addObject:@(i)];
    }
}

//loop for string and for each location change the color

NSMutableAttributedString *text = [[NSMutableAttributedString alloc]initWithString:string];
for (NSInteger i=0; i<locations.count; i++) {
    NSRange range=NSMakeRange([locations[i] intValue], 1);
    [text addAttribute:NSForegroundColorAttributeName value:[UIColor redColor] range:range];
}