Underline text in a UITextView

If this is static text, you can underline it in Interface Builder. Make sure to make the text 'Attributed' first by selecting 'Attributed' in the drop down menu:

Try to use NSAttributedString as follows and set in UITextView. This works for iOS6.

NSMutableAttributedString *attString = [[NSMutableAttributedString alloc] initWithString:@"Some String"];
[attString addAttribute:(NSString*)kCTUnderlineStyleAttributeName 
                   value:[NSNumber numberWithInt:kCTUnderlineStyleSingle] 
                   range:(NSRange){0,[attString length]}];

For more info on NSAttributedString check this How do you use NSAttributedString?

For eg:-

textView.attributedText = attString;

From apple documentation on UITextView,

In iOS 6 and later, this class supports multiple text styles through use of the attributedText property. (Styled text is not supported in earlier versions of iOS.) Setting a value for this property causes the text view to use the style information provided in the attributed string. You can still use the font, textColor, and textAlignment properties to set style attributes, but those properties apply to all of the text in the text view.

attributedText:

The styled text displayed by the text view.

@property(nonatomic,copy) NSAttributedString *attributedText

Discussion: This property is nil by default. Assigning a new value to this property also replaces the value of the text property with the same string data, albeit without any formatting information. In addition, assigning a new a value updates the values in the font, textColor, and textAlignment properties so that they reflect the style information starting at location 0 in the attributed string.

If you want to avoid having to include CoreText, you can utilize an attributed string with this attribute:

@{NSUnderlineStyleAttributeName: @(NSUnderlineStyleSingle)}