insert string in string at index (swift)

Question

I've got a text which has some HTML tags in it. Something like this:

Lorem lipsum <a href="www.example.com"> lorem lipsum.

I want to insert the text style=\"text-decoration: none\ right at the end of the HTML tag so that the link has no underline.

I've got a regex pattern that finds the HTML tag: <\s*a[^>]*>(.*?)<\s*/\s*a>

I have the following code to get the regex matches in the paragraph text and to calculate the position of the last character in the HTML tag:

let range = NSRange(location: 0, length: paragraph.utf16.count)
let regex = try! NSRegularExpression(pattern: "<\\s*a[^>]*>(.*?)<\\s*/\\s*a>")
let allMatches = regex.matches(in: paragraph, options: [], range: range)
let lastCharacter = allMatches[0].range.location + allMatches[0].range.length

How can I insert the string style=\"text-decoration: none\ at that position?

I tried something like this:

let newParagraph = paragraph.insert(" style=\"text-decoration: none\"", at: lastCharacter)

However Xcode says that the first parameter in the insert method has to be a character, not a string.

Is this an objective-c method? Xcode won't autocomplete this method. — WalterBeiter
– WalterBeiter, Commented Jul 17, 2018 at 6:58

Tom E · Accepted Answer · 2018-07-17 08:47:44Z

1

In my solution I use a regex finding everything between <and >to find the whole HTML tag. After the tag is found I use the replacingOccurrences(of:with:) method to

replace the closing tag’s bracket with the additional style= attribute (plus a closing bracket) to create the modified tag,
replace the original tag with the modified tag.

Here’s the code:

let string = "Lorem lipsum <a href=\"www.example.com\"> lorem lipsum <a href=\"www.somewhereelse.com\"> dolor sit amet."
let insertString = " style=\"text-decoration: none\">"
var modifiedString = string

let regex = try! NSRegularExpression(pattern: "<.*?>")
let range = NSRange(string.startIndex..., in: string)
let matches = regex.matches(in: string, range: range)
let tags = matches.map { String(string[Range($0.range, in: string)!]) }

for tag in tags {
    let newTag = tag.replacingOccurrences(of: ">", with: insertString)
    modifiedString = modifiedString.replacingOccurrences(of: tag, with: newTag)
}

print(modifiedString)

The updated code now uses a loop to replace all tags with the enhanced tags as per your requirement. For this to work you will have to change the regex to non-greedy: <.*?> instead of <.*>.

edited Jul 17, 2018 at 8:47

answered Jul 17, 2018 at 7:24

Tom E

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6 Comments

Tom E Over a year ago

@WalterBeiter: Ok, I've just updated my code accordingly.

WalterBeiter Over a year ago

I tried implementing your code. I'Ve stumbled upon the short regex pattern. I only want this to happen for <a> tags – links in html. Thats why I had this longer regex pattern.

Tom E Over a year ago

Sure. Just make sure your pattern is non-greedy so that you get an array of tags. So (without having tested) the pattern <a.*?> should do—or your pattern, of course ;-).

Tom E Over a year ago

Cool! Glad I could help.

Tom E Over a year ago

matches is an array of NSTextCheckingResult items returned from the regex queries. The map command traverses all array elements, exposing each element through the $0 placeholder. So $0.range effectively means <first regex match>.range, <second regex match>.range, ... NSTextCheckingResult.range yields the range of the regex match inside the search string. String(...) extracts this range from the string. map returns an array of whatever happens inside {and }, being Stringin our example. I. e. you get an array of strings each representing one of the regex matches.

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