Swift 3 & amp; 4

Это решение удаляет любые нечисловые символы перед применением форматирования. Он возвращает nil, если исходный номер телефона не может быть отформатирован в соответствии с предположениями.

Swift 4

Решение Swift 4 учитывает устаревание CharacterView и Sting, становящееся совокупностью символов

import Foundation

func format(phoneNumber sourcePhoneNumber: String) -> String? {
    // Remove any character that is not a number
    let numbersOnly = sourcePhoneNumber.components(separatedBy: CharacterSet.decimalDigits.inverted).joined()
    let length = numbersOnly.count
    let hasLeadingOne = numbersOnly.hasPrefix("1")

    // Check for supported phone number length
    guard length == 7 || length == 10 || (length == 11 && hasLeadingOne) else {
        return nil
    }

    let hasAreaCode = (length >= 10)
    var sourceIndex = 0

    // Leading 1
    var leadingOne = ""
    if hasLeadingOne {
        leadingOne = "1 "
        sourceIndex += 1
    }

    // Area code
    var areaCode = ""
    if hasAreaCode {
        let areaCodeLength = 3
        guard let areaCodeSubstring = numbersOnly.substring(start: sourceIndex, offsetBy: areaCodeLength) else {
            return nil
        }
        areaCode = String(format: "(%@) ", areaCodeSubstring)
        sourceIndex += areaCodeLength
    }

    // Prefix, 3 characters
    let prefixLength = 3
    guard let prefix = numbersOnly.substring(start: sourceIndex, offsetBy: prefixLength) else {
        return nil
    }
    sourceIndex += prefixLength

    // Suffix, 4 characters
    let suffixLength = 4
    guard let suffix = numbersOnly.substring(start: sourceIndex, offsetBy: suffixLength) else {
        return nil
    }

    return leadingOne + areaCode + prefix + "-" + suffix
}

extension String {
    /// This method makes it easier extract a substring by character index where a character is viewed as a human-readable character (grapheme cluster).
    internal func substring(start: Int, offsetBy: Int) -> String? {
        guard let substringStartIndex = self.index(startIndex, offsetBy: start, limitedBy: endIndex) else {
            return nil
        }

        guard let substringEndIndex = self.index(startIndex, offsetBy: start + offsetBy, limitedBy: endIndex) else {
            return nil
        }

        return String(self[substringStartIndex ..< substringEndIndex])
    }
}

Swift 3

import Foundation

func format(phoneNumber sourcePhoneNumber: String) -> String? {

    // Remove any character that is not a number
    let numbersOnly = sourcePhoneNumber.components(separatedBy: CharacterSet.decimalDigits.inverted).joined()
    let length = numbersOnly.characters.count
    let hasLeadingOne = numbersOnly.hasPrefix("1")

    // Check for supported phone number length
    guard length == 7 || length == 10 || (length == 11 && hasLeadingOne) else {
        return nil
    }

    let hasAreaCode = (length >= 10)
    var sourceIndex = 0

    // Leading 1
    var leadingOne = ""
    if hasLeadingOne {
        leadingOne = "1 "
        sourceIndex += 1
    }

    // Area code
    var areaCode = ""
    if hasAreaCode {
        let areaCodeLength = 3
        guard let areaCodeSubstring = numbersOnly.characters.substring(start: sourceIndex, offsetBy: areaCodeLength) else {
            return nil
        }
        areaCode = String(format: "(%@) ", areaCodeSubstring)
        sourceIndex += areaCodeLength
    }

    // Prefix, 3 characters
    let prefixLength = 3
    guard let prefix = numbersOnly.characters.substring(start: sourceIndex, offsetBy: prefixLength) else {
        return nil
    }
    sourceIndex += prefixLength

    // Suffix, 4 characters
    let suffixLength = 4
    guard let suffix = numbersOnly.characters.substring(start: sourceIndex, offsetBy: suffixLength) else {
        return nil
    }

    return leadingOne + areaCode + prefix + "-" + suffix
}

extension String.CharacterView {
    /// This method makes it easier extract a substring by character index where a character is viewed as a human-readable character (grapheme cluster).
    internal func substring(start: Int, offsetBy: Int) -> String? {
        guard let substringStartIndex = self.index(startIndex, offsetBy: start, limitedBy: endIndex) else {
            return nil
        }

        guard let substringEndIndex = self.index(startIndex, offsetBy: start + offsetBy, limitedBy: endIndex) else {
            return nil
        }

        return String(self[substringStartIndex ..< substringEndIndex])
    }
}

Пример

func testFormat(sourcePhoneNumber: String) -> String {
    if let formattedPhoneNumber = format(phoneNumber: sourcePhoneNumber) {
        return "'\(sourcePhoneNumber)' => '\(formattedPhoneNumber)'"
    }
    else {
        return "'\(sourcePhoneNumber)' => nil"
    }
}

print(testFormat(sourcePhoneNumber: "1 800 222 3333"))
print(testFormat(sourcePhoneNumber: "18002223333"))
print(testFormat(sourcePhoneNumber: "8002223333"))
print(testFormat(sourcePhoneNumber: "2223333"))
print(testFormat(sourcePhoneNumber: "18002223333444"))
print(testFormat(sourcePhoneNumber: "Letters8002223333"))

Пример вывода

'1 800 222 3333' => '1 (800) 222-3333'

'18002223333' => '1 (800) 222-3333'

'8002223333' => '(800) 222-3333'

'2223333' => '222-3333'

'18002223333444' => nil

'Letters8002223333' => '(800) 222-3333'