Underlining text in UIButton

From iOS6 it is now possible to use an NSAttributedString to perform underlining (and anything else attributed strings support) in a much more flexible way:

NSMutableAttributedString *commentString = [[NSMutableAttributedString alloc] initWithString:@"The Quick Brown Fox"];

[commentString addAttribute:NSUnderlineStyleAttributeName value:[NSNumber numberWithInteger:NSUnderlineStyleSingle] range:NSMakeRange(0, [commentString length])];

[button setAttributedTitle:commentString forState:UIControlStateNormal];

Note: added this as another answer - as its a totally different solution to my previous one.

Edit: oddly (in iOS8 at least) you have to underline the first character otherwise it doesn't work!

so as a workaround, set the first char underlined with clear colour!

    // underline Terms and condidtions
    NSMutableAttributedString* tncString = [[NSMutableAttributedString alloc] initWithString:@"View Terms and Conditions"];

    // workaround for bug in UIButton - first char needs to be underlined for some reason!
    [tncString addAttribute:NSUnderlineStyleAttributeName
                      value:@(NSUnderlineStyleSingle)
                      range:(NSRange){0,1}];
    [tncString addAttribute:NSUnderlineColorAttributeName value:[UIColor clearColor] range:NSMakeRange(0, 1)];


    [tncString addAttribute:NSUnderlineStyleAttributeName
                      value:@(NSUnderlineStyleSingle)
                      range:(NSRange){5,[tncString length] - 5}];

    [tncBtn setAttributedTitle:tncString forState:UIControlStateNormal];

To use interface builder to underline, one has to:

• Change it to attributed
• Highlight the text in the Attributes inspector
• Right click, choose Font and then Underline

Video someone else made https://www.youtube.com/watch?v=5-ZnV3jQd9I