这是我的十六进制字符串到数据例程：

This is my hex string to Data routine:

extension String {

    /// Create `Data` from hexadecimal string representation
    ///
    /// This takes a hexadecimal representation and creates a `Data` object. Note, if the string has any spaces or non-hex characters (e.g. starts with '<' and with a '>'), those are ignored and only hex characters are processed.
    ///
    /// - returns: Data represented by this hexadecimal string.

    func hexadecimal() -> Data? {
        var data = Data(capacity: characters.count / 2)

        let regex = try! NSRegularExpression(pattern: "[0-9a-f]{1,2}", options: .caseInsensitive)
        regex.enumerateMatches(in: self, range: NSMakeRange(0, utf16.count)) { match, flags, stop in
            let byteString = (self as NSString).substring(with: match!.range)
            var num = UInt8(byteString, radix: 16)!
            data.append(&num, count: 1)
        }

        guard data.count > 0 else { return nil }

        return data
    }

}

为了完整起见，这是我的数据到十六进制字符串例程：

And for the sake of completeness, this is my Data to hex string routine:

extension Data {

    /// Create hexadecimal string representation of `Data` object.
    ///
    /// - returns: `String` representation of this `Data` object.

    func hexadecimal() -> String {
        return map { String(format: "%02x", $0) }
            .joined(separator: "")
    }
}

注意，如上所示，我通常只在十六进制表示和 NSData 实例（因为如果信息可能已经表示为字符串，那么您可能不会首先创建十六进制表示）。但是您的原始问题想要在十六进制表示和 String 对象之间进行转换，这可能是这样的：

Note, as shown in the above, I generally only convert between hexadecimal representations and NSData instances (because if the information could have been represented as a string you probably wouldn't have created a hexadecimal representation in the first place). But your original question wanted to convert between hexadecimal representations and String objects, and that might look like so:

extension String {

    /// Create `String` representation of `Data` created from hexadecimal string representation
    ///
    /// This takes a hexadecimal representation and creates a String object from that. Note, if the string has any spaces, those are removed. Also if the string started with a `<` or ended with a `>`, those are removed, too.
    ///
    /// For example,
    ///
    ///     String(hexadecimal: "<666f6f>")
    ///
    /// is
    ///
    ///     Optional("foo")
    ///
    /// - returns: `String` represented by this hexadecimal string.

    init?(hexadecimal string: String, encoding: String.Encoding = .utf8) {
        guard let data = string.hexadecimal() else {
            return nil
        }

        self.init(data: data, encoding: encoding)
    }

    /// Create hexadecimal string representation of `String` object.
    ///
    /// For example,
    ///
    ///     "foo".hexadecimalString()
    ///
    /// is
    ///
    ///     Optional("666f6f")
    ///
    /// - parameter encoding: The `String.Encoding` that indicates how the string should be converted to `Data` before performing the hexadecimal conversion.
    ///
    /// - returns: `String` representation of this String object.

    func hexadecimalString(encoding: String.Encoding = .utf8) -> String? {
        return data(using: encoding)?
            .hexadecimal()
    }

}

然后你就可以像上面那样使用上面的内容：

You could then use the above like so:

let hexString = "68656c6c 6f2c2077 6f726c64"
print(String(hexadecimal: hexString))

或者，

let originalString = "hello, world"
print(originalString.hexadecimalString())

对于早期Swift版本的上述排列，请参阅此问题的修订历史记录。

For permutations of the above for earlier Swift versions, see the revision history of this question.