CODEWITHSUNDEEP
iosswiftxcodensstring
user1107173
user1107173

Reputation: 10744

Swift: Get an index of beginning and ending character of a word in a String

A string:

"[email protected], [email protected], [email protected], [email protected]"

Through gesture recognizer, I am able to get the character the user tapped on (happy to provide code, but don't see the relevance at this point).

Let's say the User tapped on o in "[email protected]" and the character index is 39

Given 39 the index of o, I would like to get the string start index of c where "[email protected]" begins, and an end index for m from "com" where "[email protected]" ends.

In another words, given an index of a character in a String, I need to get the index on the left and right right before we encounter a space in a String on the left and a comma on the right.

Tried, but this only provides the last word in the String:

if let range = text.range(of: " ", options: .backwards) {
  let suffix = String(text.suffix(from: range.upperBound)) 
  print(suffix) // [email protected]
}

I am not sure where to go from here?

Upvotes: 2

Views: 2229

Answers (3)

Martin R
Martin R

Reputation: 539735

You can call range(of:) on two slices of the given string: text[..<index] is the text preceding the given character position, and text[index...] is the text starting at the given position.

Example:

let text = "[email protected], [email protected], [email protected], [email protected]"
let index = text.index(text.startIndex, offsetBy: 39)

// Search the space before the given position:
let start = text[..<index].range(of: " ", options: .backwards)?.upperBound ?? text.startIndex

// Search the comma after the given position: 
let end = text[index...].range(of: ",")?.lowerBound ?? text.endIndex

print(text[start..<end]) // [email protected]

Both range(of:) calls return nil if no space (or comma) has been found. In that case the nil-coalescing operator ?? is used to get the start (or end) index instead.

(Note that this works because Substrings share a common index with their originating string.)

An alternative approach is to use a "data detector", so that the URL detection does not depend on certain separators.

Example (compare How to detect a URL in a String using NSDataDetector):

let text = "[email protected], [email protected], [email protected], [email protected]"
let index = text.index(text.startIndex, offsetBy: 39)

let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
let matches = detector.matches(in: text, range: NSRange(location: 0, length: text.utf16.count))

for match in matches {
    if let range = Range(match.range, in: text), range.contains(index) {
        print(text[range])
    }
}

Upvotes: 5

vadian
vadian

Reputation: 285079

Different approach:

You have the string and the Int index

let string = "[email protected], [email protected], [email protected], [email protected]"
let characterIndex = 39

Get the String.Index from the Int

let stringIndex = string.index(string.startIndex, offsetBy: characterIndex)

Convert the string into an array of addresses

let addresses = string.components(separatedBy: ", ")

Map the addresses to their ranges (Range<String.Index>) in the string

let ranges = addresses.map{string.range(of: $0)!}

Get the (Int) index of the range which contains stringIndex

if let index = ranges.index(where: {$0.contains(stringIndex)}) {

Get the corresponding address

let address = addresses[index] }

Upvotes: 2

Joakim Danielson
Joakim Danielson

Reputation: 51891

One approach could be to split the original string on the “,” and then using simple math to find in what element of the array the given position (39) exist and from there get the right string or indexes for the previous space and next comma depending on what your end goal is.

Upvotes: 0

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