Adding a Dotted red line under characters in a UITextView

Question

I am trying to create my custom spell checker for the UITextView.
To show that a word is misspelled, I need to add the "red dotted line" under the misspelled word. To do that, here is what I thought would work -
I create a dictionary which contains the values for the key NSUnderlineStyleAttributeName. However, what this does is, it does underline the characters but it does not have a dotted pattern. Also, setting the strokeColorAttribute also does not seem to have any effect.
Here is my code -
NSMutableDictionary *misspelledAttributes = [NSMutableDictionary dictionary];
[misspelledAttributes setObject:[NSNumber numberWithInt:kCTUnderlineStyleThick|kCTUnderlinePatternDot] forKey:NSUnderlineStyleAttributeName];
[misspelledAttributes setObject:[UIColor redColor] forKey:NSStrokeColorAttributeName];
To set the attributes to a attributed string for a particular range -
NSMutableAttributedString *attrString = [self.textView.attributedText mutableCopy];
[attrString addAttributes:misspelledAttributes range:wordRange];
self.textView.scrollEnabled = NO;
self.textView.attributedText = attrString;
self.textView.selectedRange = NSMakeRange(NSMaxRange(range), 0);
self.textView.scrollEnabled = YES;

Answer 1

I agree that the NSStrokeColorAttributeName is not the correct property to use. I am not able to edit my post to remove that piece of code.
I am trying to do this for my iOS project and NSUnderlineColorAttributeName is not available for iOS yet. It is only available for OSX. I just checked that in the developer library.
Am I missing something here?
Also, I am unable to add a "dotted" underline. All I can do is put a single line under the text. is Apple allowing us to only put a single line and not any of the other types of underline styles such as dashed, dotted etc.?