Underline part of a string using NSMutableAttributedString in iOS 8 is not working

Update: By investigating this question: Displaying NSMutableAttributedString on iOS 8 I finally found the solution!

You should add NSUnderlineStyleNone at the beginning of the string.

Swift 4.2 (none was removed):

let attributedString = NSMutableAttributedString()
attributedString.append(NSAttributedString(string: "test ",
                                           attributes: [.underlineStyle: 0]))
attributedString.append(NSAttributedString(string: "s",
                                           attributes: [.underlineStyle: NSUnderlineStyle.single.rawValue]))
attributedString.append(NSAttributedString(string: "tring",
                                           attributes: [.underlineStyle: 0]))

Objective-C:

 NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] init];
 [attributedString appendAttributedString:[[NSAttributedString alloc] initWithString:@"test "
                                                                          attributes:@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleNone)}]];
 [attributedString appendAttributedString:[[NSAttributedString alloc] initWithString:@"s"
                                                                         attributes:@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleSingle),
                                                                                      NSBackgroundColorAttributeName: [UIColor clearColor]}]];
 [attributedString appendAttributedString:[[NSAttributedString alloc] initWithString:@"tring"]];

Another bonus of such approach is absence of any ranges. Very nice for localized strings.

Seems like it is Apple bug :(

I found that if you apply UnderlineStyleNone to the whole string you can then selectively apply underline to a part that starts in the middle:

func underlinedString(string: NSString, term: NSString) -> NSAttributedString {
    let output = NSMutableAttributedString(string: string)
    let underlineRange = string.rangeOfString(term)
    output.addAttribute(NSUnderlineStyleAttributeName, value: NSUnderlineStyle.StyleNone.rawValue, range: NSMakeRange(0, string.length))
    output.addAttribute(NSUnderlineStyleAttributeName, value: NSUnderlineStyle.StyleSingle.rawValue, range: underlineRange)

    return output
}

NSMutableAttributedString *signUpString = [[NSMutableAttributedString alloc] initWithString:@"Not a member yet?Sign Up now"];

[signUpString appendAttributedString:[[NSAttributedString alloc] initWithString:@" "attributes:@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleNone)}]];

[signUpString addAttributes: @{NSForegroundColorAttributeName:UIColorFromRGB(0x43484B),NSUnderlineStyleAttributeName:[NSNumber numberWithInteger:NSUnderlineStyleSingle]} range:NSMakeRange(17,11)];

signUpLbl.attributedText = [signUpString copy];

It worked for me