¿Cómo decodifico entidades HTML en Swift?

Estoy extrayendo un archivo JSON de un sitio y una de las cadenas recibidas es:

The Weeknd &#8216;King Of The Fall&#8217; [Video Premiere] | @TheWeeknd | #SoPhi

¿ Cómo puedo convertir cosas como &#8216en los caracteres correctos?

Hice un Xcode Playground para demostrarlo:

import UIKit

var error: NSError?
let blogUrl: NSURL = NSURL.URLWithString("http://sophisticatedignorance.net/api/get_recent_summary/")
let jsonData = NSData(contentsOfURL: blogUrl)

let dataDictionary = NSJSONSerialization.JSONObjectWithData(jsonData, options: nil, error: &error) as NSDictionary

var a = dataDictionary["posts"] as NSArray

println(a[0]["title"])

Sep 01 '14 20:09 code_cookies

Esta respuesta se revisó por última vez para Swift 5.2 y iOS 13.4 SDK.

No existe una forma sencilla de hacerlo, pero puedes usar NSAttributedStringmagia para que este proceso sea lo más sencillo posible (ten en cuenta que este método también eliminará todas las etiquetas HTML).

Recuerde inicializar NSAttributedStringúnicamente desde el hilo principal . Utiliza WebKit para analizar el HTML subyacente, de ahí el requisito.

// This is a[0]["title"] in your case
let htmlEncodedString = "The Weeknd <em>&#8216;King Of The Fall&#8217;</em>"

guard let data = htmlEncodedString.data(using: .utf8) else {
    return
}

let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [
    .documentType: NSAttributedString.DocumentType.html,
    .characterEncoding: String.Encoding.utf8.rawValue
]

guard let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) else {
    return
}

// The Weeknd ‘King Of The Fall’
let decodedString = attributedString.string

extension String {

    init?(htmlEncodedString: String) {

        guard let data = htmlEncodedString.data(using: .utf8) else {
            return nil
        }

        let options: [NSAttributedString.DocumentReadingOptionKey: Any] = [
            .documentType: NSAttributedString.DocumentType.html,
            .characterEncoding: String.Encoding.utf8.rawValue
        ]

        guard let attributedString = try? NSAttributedString(data: data, options: options, documentAttributes: nil) else {
            return nil
        }

        self.init(attributedString.string)

    }

}

let encodedString = "The Weeknd <em>&#8216;King Of The Fall&#8217;</em>"
let decodedString = String(htmlEncodedString: encodedString)

Sep 01 '2014 14:09 akashivskyy

La respuesta de @akashivskyy es excelente y demuestra cómo utilizarla NSAttributedStringpara decodificar entidades HTML. Una posible desventaja (como dijo) es que también se elimina todo el marcado HTML, por lo que

<strong> 4 &lt; 5 &amp; 3 &gt; 2</strong>

se convierte

4 < 5 & 3 > 2

En OS X existe CFXMLCreateStringByUnescapingEntities()el que hace el trabajo:

let encoded = "<strong> 4 &lt; 5 &amp; 3 &gt; 2 .</strong> Price: 12 &#x20ac;.  &#64; "
let decoded = CFXMLCreateStringByUnescapingEntities(nil, encoded, nil) as String
println(decoded)
// <strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €.  @

pero esto no está disponible en iOS.

Aquí hay una implementación Swift pura. Decodifica referencias de entidades de caracteres, como <usar un diccionario, y todas las entidades de caracteres numéricos, como &#64o &#x20ac. (Tenga en cuenta que no enumeré explícitamente las 252 entidades HTML).

Rápido 4:

// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ Substring : Character ] = [
    // XML predefined entities:
    "&quot;"    : "\"",
    "&amp;"     : "&",
    "&apos;"    : "'",
    "&lt;"      : "<",
    "&gt;"      : ">",

    // HTML character entity references:
    "&nbsp;"    : "\u{00a0}",
    // ...
    "&diams;"   : "♦",
]

extension String {

    /// Returns a new string made by replacing in the `String`
    /// all HTML character entity references with the corresponding
    /// character.
    var stringByDecodingHTMLEntities : String {

        // ===== Utility functions =====

        // Convert the number in the string to the corresponding
        // Unicode character, e.g.
        //    decodeNumeric("64", 10)   --> "@"
        //    decodeNumeric("20ac", 16) --> "€"
        func decodeNumeric(_ string : Substring, base : Int) -> Character? {
            guard let code = UInt32(string, radix: base),
                let uniScalar = UnicodeScalar(code) else { return nil }
            return Character(uniScalar)
        }

        // Decode the HTML character entity to the corresponding
        // Unicode character, return `nil` for invalid input.
        //     decode("&#64;")    --> "@"
        //     decode("&#x20ac;") --> "€"
        //     decode("&lt;")     --> "<"
        //     decode("&foo;")    --> nil
        func decode(_ entity : Substring) -> Character? {

            if entity.hasPrefix("&#x") || entity.hasPrefix("&#X") {
                return decodeNumeric(entity.dropFirst(3).dropLast(), base: 16)
            } else if entity.hasPrefix("&#") {
                return decodeNumeric(entity.dropFirst(2).dropLast(), base: 10)
            } else {
                return characterEntities[entity]
            }
        }

        // ===== Method starts here =====

        var result = ""
        var position = startIndex

        // Find the next '&' and copy the characters preceding it to `result`:
        while let ampRange = self[position...].range(of: "&") {
            result.append(contentsOf: self[position ..< ampRange.lowerBound])
            position = ampRange.lowerBound

            // Find the next ';' and copy everything from '&' to ';' into `entity`
            guard let semiRange = self[position...].range(of: ";") else {
                // No matching ';'.
                break
            }
            let entity = self[position ..< semiRange.upperBound]
            position = semiRange.upperBound

            if let decoded = decode(entity) {
                // Replace by decoded character:
                result.append(decoded)
            } else {
                // Invalid entity, copy verbatim:
                result.append(contentsOf: entity)
            }
        }
        // Copy remaining characters to `result`:
        result.append(contentsOf: self[position...])
        return result
    }
}

Ejemplo:

let encoded = "<strong> 4 &lt; 5 &amp; 3 &gt; 2 .</strong> Price: 12 &#x20ac;.  &#64; "
let decoded = encoded.stringByDecodingHTMLEntities
print(decoded)
// <strong> 4 < 5 & 3 > 2 .</strong> Price: 12 €.  @

Rápido 3:

// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ String : Character ] = [
    // XML predefined entities:
    "&quot;"    : "\"",
    "&amp;"     : "&",
    "&apos;"    : "'",
    "&lt;"      : "<",
    "&gt;"      : ">",

    // HTML character entity references:
    "&nbsp;"    : "\u{00a0}",
    // ...
    "&diams;"   : "♦",
]

extension String {

    /// Returns a new string made by replacing in the `String`
    /// all HTML character entity references with the corresponding
    /// character.
    var stringByDecodingHTMLEntities : String {

        // ===== Utility functions =====

        // Convert the number in the string to the corresponding
        // Unicode character, e.g.
        //    decodeNumeric("64", 10)   --> "@"
        //    decodeNumeric("20ac", 16) --> "€"
        func decodeNumeric(_ string : String, base : Int) -> Character? {
            guard let code = UInt32(string, radix: base),
                let uniScalar = UnicodeScalar(code) else { return nil }
            return Character(uniScalar)
        }

        // Decode the HTML character entity to the corresponding
        // Unicode character, return `nil` for invalid input.
        //     decode("&#64;")    --> "@"
        //     decode("&#x20ac;") --> "€"
        //     decode("&lt;")     --> "<"
        //     decode("&foo;")    --> nil
        func decode(_ entity : String) -> Character? {

            if entity.hasPrefix("&#x") || entity.hasPrefix("&#X"){
                return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 3) ..< entity.index(entity.endIndex, offsetBy: -1)), base: 16)
            } else if entity.hasPrefix("&#") {
                return decodeNumeric(entity.substring(with: entity.index(entity.startIndex, offsetBy: 2) ..< entity.index(entity.endIndex, offsetBy: -1)), base: 10)
            } else {
                return characterEntities[entity]
            }
        }

        // ===== Method starts here =====

        var result = ""
        var position = startIndex

        // Find the next '&' and copy the characters preceding it to `result`:
        while let ampRange = self.range(of: "&", range: position ..< endIndex) {
            result.append(self[position ..< ampRange.lowerBound])
            position = ampRange.lowerBound

            // Find the next ';' and copy everything from '&' to ';' into `entity`
            if let semiRange = self.range(of: ";", range: position ..< endIndex) {
                let entity = self[position ..< semiRange.upperBound]
                position = semiRange.upperBound

                if let decoded = decode(entity) {
                    // Replace by decoded character:
                    result.append(decoded)
                } else {
                    // Invalid entity, copy verbatim:
                    result.append(entity)
                }
            } else {
                // No matching ';'.
                break
            }
        }
        // Copy remaining characters to `result`:
        result.append(self[position ..< endIndex])
        return result
    }
}

Rápido 2:

// Mapping from XML/HTML character entity reference to character
// From http://en.wikipedia.org/wiki/List_of_XML_and_HTML_character_entity_references
private let characterEntities : [ String : Character ] = [
    // XML predefined entities:
    "&quot;"    : "\"",
    "&amp;"     : "&",
    "&apos;"    : "'",
    "&lt;"      : "<",
    "&gt;"      : ">",

    // HTML character entity references:
    "&nbsp;"    : "\u{00a0}",
    // ...
    "&diams;"   : "♦",
]

extension String {

    /// Returns a new string made by replacing in the `String`
    /// all HTML character entity references with the corresponding
    /// character.
    var stringByDecodingHTMLEntities : String {

        // ===== Utility functions =====

        // Convert the number in the string to the corresponding
        // Unicode character, e.g.
        //    decodeNumeric("64", 10)   --> "@"
        //    decodeNumeric("20ac", 16) --> "€"
        func decodeNumeric(string : String, base : Int32) -> Character? {
            let code = UInt32(strtoul(string, nil, base))
            return Character(UnicodeScalar(code))
        }

        // Decode the HTML character entity to the corresponding
        // Unicode character, return `nil` for invalid input.
        //     decode("&#64;")    --> "@"
        //     decode("&#x20ac;") --> "€"
        //     decode("&lt;")     --> "<"
        //     decode("&foo;")    --> nil
        func decode(entity : String) -> Character? {

            if entity.hasPrefix("&#x") || entity.hasPrefix("&#X"){
                return decodeNumeric(entity.substringFromIndex(entity.startIndex.advancedBy(3)), base: 16)
            } else if entity.hasPrefix("&#") {
                return decodeNumeric(entity.substringFromIndex(entity.startIndex.advancedBy(2)), base: 10)
            } else {
                return characterEntities[entity]
            }
        }

        // ===== Method starts here =====

        var result = ""
        var position = startIndex

        // Find the next '&' and copy the characters preceding it to `result`:
        while let ampRange = self.rangeOfString("&", range: position ..< endIndex) {
            result.appendContentsOf(self[position ..< ampRange.startIndex])
            position = ampRange.startIndex

            // Find the next ';' and copy everything from '&' to ';' into `entity`
            if let semiRange = self.rangeOfString(";", range: position ..< endIndex) {
                let entity = self[position ..< semiRange.endIndex]
                position = semiRange.endIndex

                if let decoded = decode(entity) {
                    // Replace by decoded character:
                    result.append(decoded)
                } else {
                    // Invalid entity, copy verbatim:
                    result.appendContentsOf(entity)
                }
            } else {
                // No matching ';'.
                break
            }
        }
        // Copy remaining characters to `result`:
        result.appendContentsOf(self[position ..< endIndex])
        return result
    }
}

May 09 '2015 15:05 Martin R