Adding attributes to string with emojis breaks some emojis

Question

When I'm trying to add attributes to attributed string that contains emojis sometimes some of emojis are broken. For regular text works perfectly. Any ideas what am I doing wrong?

Here is my function - it should bold quotations (text between first and last quotation mark)

func boldQuotation(str: String, fontSize: CGFloat) -> NSAttributedString {
    let normalAttributes = [NSFontAttributeName : UIFont.systemFontOfSize(fontSize)]
    let boldAttributes = [NSFontAttributeName : UIFont.boldSystemFontOfSize(fontSize)]
    let attributedStr = NSMutableAttributedString(string: str, attributes: normalAttributes)

    let firstQuotationMarkRange = str.rangeOfString("\"")
    let lastQuotationMarkRange  = str.rangeOfString("\"", options: [.BackwardsSearch], range: nil, locale: nil)
    guard let firstIndex = firstQuotationMarkRange?.startIndex, lastIndex = lastQuotationMarkRange?.endIndex else {
        return attributedStr
    }
    attributedStr.addAttributes(boldAttributes, range: NSMakeRange(str.startIndex.distanceTo(firstIndex), firstIndex.distanceTo(lastIndex)))
    return attributedStr
}

Here is sample of text that cannot be correctly attributed:

let str = "\"\""

The result looks like this:

I'm using Swift 2.3, iOS 10.2.1 , Xcode 8.2.1, Deployment target: 9.3

score 0 · Answer 1 · edited May 23 '17 at 11:47

Ok, after further investigation (and no answer) I finally found reason and solution of that bug.

There was a problem with creation NSRange using indices of Range (obtained from String). Long story short - Swift String ranges and NSString ranges shouldn't be used to converting one to another. At least not like this:

let firstQuotationMarkRange     = str.rangeOfString("\"")
let lastQuotationMarkRange      = str.rangeOfString("\"", options: [.BackwardsSearch], range: nil, locale: nil)
guard let firstIndex = firstQuotationMarkRange?.startIndex, lastIndex = lastQuotationMarkRange?.endIndex else {
        return attributedStr
    }
//THIS IS WRONG:
range = NSMakeRange(str.startIndex.distanceTo(firstIndex), firstIndex.distanceTo(lastIndex))

So what's the correct solution? Convert String to NSString first and then start looking for substring range. Here is fixed function:

func boldQuotation(str: String, fontSize: CGFloat) -> NSAttributedString {
    let normalAttributes = [NSFontAttributeName : UIFont.systemFontOfSize(fontSize)]
    let boldAttributes = [NSFontAttributeName : UIFont.boldSystemFontOfSize(fontSize)]
    let attributedStr = NSMutableAttributedString(string: str, attributes: normalAttributes)

    let nsStr = str as NSString
    let firstQuotationMarkRange = nsStr.rangeOfString("\"")
    let lastQuotationMarkRange  = nsStr.rangeOfString("\"", options: [.BackwardsSearch])
    guard firstQuotationMarkRange.length > 0 && lastQuotationMarkRange.length > 0 else {
        return attributedStr
    }
    let nsrange = NSMakeRange(firstQuotationMarkRange.location, lastQuotationMarkRange.location + lastQuotationMarkRange.length - firstQuotationMarkRange.location)
    attributedStr.addAttributes(boldAttributes, range: nsrange)
    return attributedStr
}

Solved thanks to this post: NSRange from Swift Range

Adding attributes to string with emojis breaks some emojis

1 Answers1