Do simple +stringWithFormat:-type operations with NSAttributedString.

NSAttributedString+format.m

//
//  NSAttributedString+format.m
//  Chatterbox
//
//  Created by Brent Royal-Gordon on 2/7/14.
//  Copyright (c) 2014 Architechies. All rights reserved.
//

#import "NSAttributedString+format.h"

@implementation NSAttributedString (format)

- (instancetype)initWithFormat:(NSString *)format attributes:(NSDictionary *)attrs argumentAttributes:(NSDictionary *)argAttrs arguments:(va_list)argList {
    NSMutableAttributedString * text = [[NSMutableAttributedString alloc] initWithString:@"" attributes:attrs];
    NSScanner * scanner = [NSScanner scannerWithString:format];
    scanner.charactersToBeSkipped = [NSCharacterSet new];
    
    while (![scanner isAtEnd]) {
        NSString * discarded;
        
        [scanner scanUpToString:@"%" intoString:&discarded];
        if(discarded) {
            [text appendAttributedString:[[NSAttributedString alloc] initWithString:discarded attributes:attrs]];
        }
        
        if([scanner scanString:@"%%" intoString:NULL]) {
            [text appendAttributedString:[[NSAttributedString alloc] initWithString:@"%" attributes:attrs]];
        }
        else if([scanner scanString:@"%@" intoString:NULL]) {
            id object = va_arg(argList, id);
            if(![object isKindOfClass:NSAttributedString.class]) {
                object = [[NSAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@", object] attributes:argAttrs];
            }
            [text appendAttributedString:object];
        }
        else if([scanner scanString:@"%" intoString:NULL]) {
            NSString * specifier = [format substringFromIndex:scanner.scanLocation];
            if(specifier.length > 1) {
                specifier = [specifier substringToIndex:1];
            }
            NSAssert(NO, @"Unsupported format specifier '%@'", specifier);
        }
    }
    
    return text;
}

- (instancetype)initWithFormat:(NSString *)format attributes:(NSDictionary *)attrs argumentAttributes:(NSDictionary *)argAttrs, ... {
    va_list args;
    va_start(args, argAttrs);
    NSAttributedString * text = [self initWithFormat:format attributes:attrs argumentAttributes:argAttrs arguments:args];
    va_end(args);
    
    return text;
}

@end

Very nice!

My approach to this was a constructor with a regexp, %(\d+)\$@, and an array of attributed strings to interpolate.

Really like the concept, but having an issue va_arg(argList, id) going to nil on the second object, is NSDictionary correct? Is there an example that implements this category?

Hello @brentax, is it allowed to use this gist in source code of a commercial application?