NSAttributedString with strikethrough

First, the value for NSStrikethroughStyleAttributeName must be an NSNumber, not a simple integer. Second, I think you have to include NSUnderlineStyleSingle:

...:[NSDictionary dictionaryWithObjectsAndKeys:
      ..., 
      [NSNumber numberWithInteger:NSUnderlinePatternSolid | NSUnderlineStyleSingle], 
      NSStrikethroughStyleAttributeName, 
      nil]...

Swift 4:

NSAttributedString(string: "test string", attributes: [.strikethroughStyle: NSUnderlineStyle.styleSingle.rawValue])

Swift 5:

NSAttributedString(string: "test string", attributes: [.strikethroughStyle: NSUnderlineStyle.single.rawValue])

Mind the fact that .strikethroughStyle and .underlineStyle expect an integer value (specifically an NSNumber), therefore we're using NSUnderlineStyle's .rawValue in the examples. (Setting NSUnderlineStyle causes unrecogognized selector exception)

func addAttributes(attrs: [String : AnyObject], range: NSRange)

NSUnderlineStyleAttributeName: The value of this attribute is an NSNumber object containing an integer.

Since the NSUnderlineStyle enum's rawValue is Int Type, you should initialize a NSNumber Object with it

Swift2.1:

attrStr.addAttributes([NSStrikethroughStyleAttributeName: NSNumber(integer: NSUnderlineStyle.StyleSingle.rawValue)], range: NSMakeRange(x, y))

x is the location, the start of your text

y is the length of the text

You can also simply use:

NSAttributedString *theAttributedString;
theAttributedString = [[NSAttributedString alloc] initWithString:theString 
            attributes:@{NSStrikethroughStyleAttributeName:
            [NSNumber numberWithInteger:NSUnderlineStyleSingle]}];

Update :

Swift 2.0 version

let theAttributedString = NSAttributedString(string: theString, attributes: [NSStrikethroughColorAttributeName: NSUnderlineStyle.StyleSingle])