NSString category to validate contents as Twitter username.

gistfile1.m

@interface NSString (CLUTwitterAdditions)
- (BOOL)isValidTwitterUsername;
@end
 
@implementation NSString (CLUTwitterAdditions)
 
static NSString* CLUTwitterUsernamePattern = @"^([0-9a-zA-Z_]{1,15})$";

// NB - largely yoinked from http://stackoverflow.com/questions/4424179/twitter-username-regex-validation/4424288#4424288
- (BOOL)isValidTwitterUsername {
    static NSRegularExpression* usernameRegularExpression;
    if (!usernameRegularExpression) {
        usernameRegularExpression = [NSRegularExpression regularExpressionWithPattern:CLUTwitterUsernamePattern options:NSRegularExpressionCaseInsensitive error:nil];
    }
    NSUInteger numberOfMatches = [usernameRegularExpression numberOfMatchesInString:self options:0 range:NSMakeRange(0, self.length)];
    return numberOfMatches == 1;
}
 
@end