Changing font of strings separated by spaces - ios

Question

I'm trying to make the words split by spaces green in a UITextField, kind of like the way it works when you compose of a new iMessage. I commented out the part of my code that's giving me a runtime error. Please let me know if you have any ideas:
func textChanged(sender : UITextField) {
var myMutableString = NSMutableAttributedString()
let arr = sender.text!.componentsSeparatedByString(" ")
var c = 0
for i in arr {
/*
myMutableString.addAttribute(NSForegroundColorAttributeName, value: UIColor.greenColor(), range: NSRange(location:c,length:i.characters.count))
sender.attributedText = myMutableString
*/
print(c,i.characters.count)
c += i.characters.count + 1
}
}

Answer 1

Your code has at least two parts needed to be fixed.
var myMutableString = NSMutableAttributedString()
This line creates an empty NSMutableAttributedString. Any access to the content may cause runtime error.
The other is i.characters.count. You should not use Character based locations and counts, when the APIs you want use is based on the behaviour of NSString. Use UTF-16 based count.
And one more, this is not critical, but you should use sort of meaningful names for variables.
So, all included:
func textChanged(sender: UITextField) {
let text = sender.text ?? ""
let myMutableString = NSMutableAttributedString(string: text)
let components = text.componentsSeparatedByString(" ")
var currentPosition = 0
for component in components {
myMutableString.addAttribute(NSForegroundColorAttributeName, value: UIColor.greenColor(), range: NSRange(location: currentPosition,length: component.utf16.count))
sender.attributedText = myMutableString
print(currentPosition, component.utf16.count)
currentPosition += component.utf16.count + 1
}
}
But whether this works as you expect or not depends on when this method is called.

Answer 2

You create an empty attributed string but never install any text into it.
The addAttribute call apples attributes to text in a string. If you try to apply attributes to a range that does not contain text, you will crash.
You need to install the content of the unattributed string into the attributed string, then apply attributes.
Note that you should probably move the line
sender.attributedText = myMutableString
Outside of your for loop. There is no good reason to install the attributed string to the text field repeatedly as you add color attributes to each word.
Note this bit from the Xcode docs on addAttribute:
Raises... an NSRangeException if any part of aRange lies beyond the
end of the receiver’s characters.
If you are getting an NSRangeException that would be a clue as to what is wrong with your current code. Pay careful attention to the error messages you get. They usually offer important clues as to what's going wrong.