NSAttributedString: underline is not applied - ios

Question

I'm trying to add underline style for UITextView and it's not applied. If i use "shadow" (uncomment shadow styling and comment underline styling) i can see it, but no underline is applied for some reason. I use "Courier New" font.
- (void) addDiagHighlighting: (NSMutableAttributedString*)attrString start:(int)start end:(int)end severity:(int)severity {
// ignore diags that are out of bounds
if (start > attrString.length || end > attrString.length)
return;
NSRange range = NSMakeRange(start, end - start);
UIColor *diagColor = [self getSeverityColor: severity];
// shadow
// NSShadow *shadow = [[NSShadow alloc] init];
// [shadow setShadowColor: diagColor];
// [shadow setShadowOffset: CGSizeMake (1.0, 1.0)];
// [shadow setShadowBlurRadius: 1.0];
// [attrString addAttribute:NSShadowAttributeName
// value:shadow
// range:range];
// underline
[attrString addAttributes:#{
NSUnderlineColorAttributeName : diagColor, // color
NSUnderlineStyleAttributeName : #(NSUnderlinePatternSolid) // style
}
range:range];
}
i can change adding attributes to adding both shadow and underling and i can see shadow but still no underline:
// shadow + underline
[attrString addAttributes:#{
NSShadowAttributeName : shadow, // shadow
NSUnderlineColorAttributeName : diagColor, // color
NSUnderlineStyleAttributeName : #(NSUnderlinePatternSolid) // style
}
range:range];

Answer 1

You need to OR a NSUnderlinePattern with an NSUnderlineStyle to get it working (see Apple documentation here)
Try this:
[attrString addAttributes:#{
NSShadowAttributeName : shadow, // shadow
NSUnderlineColorAttributeName : diagColor, // color
NSUnderlineStyleAttributeName : #(NSUnderlineStyleSingle | NSUnderlinePatternSolid) // style
}
range:range];
Or with dots...
[attrString addAttributes:#{
NSShadowAttributeName : shadow, // shadow
NSUnderlineColorAttributeName : diagColor, // color
NSUnderlineStyleAttributeName : #(NSUnderlineStyleSingle | NSUnderlinePatternDot) // style
}
range:range];

Answer 2

The Apple Developer Documentation states about NSUnderlineStyle:
The style, pattern, and optionally by-word mask are OR'd together to produce the value for underlineStyle and strikethroughStyle.
Therefore, with Swift 5 and iOS 12.3, you can use the bitwise OR operator (|) to set a style and a pattern together for NSAttributedString.Key.underlineStyle attribute.
The following Playground sample code shows how to set both NSUnderlineStyle.thick and NSUnderlineStyle.patternDot attributes for a NSAttributedString instance:
import UIKit
import PlaygroundSupport
let attributes = [NSAttributedString.Key.underlineStyle : (NSUnderlineStyle.thick.rawValue | NSUnderlineStyle.patternDot.rawValue)]
let attributedString = NSAttributedString(string: "Some text", attributes: attributes)
let label = UILabel(frame: CGRect(x: 0, y: 0, width: 200, height: 40))
label.backgroundColor = .white
label.attributedText = attributedString
PlaygroundPage.current.liveView = label