问Keychain persistent data iOS

EN

func savePassword(password: String, inKeychainItem: NSData?) -> NSData?
func getPasswordWithPersistentReference(persistentReference: NSData) -> String?

func savePassword(password: String, inKeychainItem: NSData?) -> NSData? {
        guard let passwordData = password.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false) else { return nil }
        var status = errSecSuccess

        if let persistentReference = inKeychainItem {
            // A persistent reference was given, update the corresponding keychain item.
            let query: [NSObject: AnyObject] = [
                kSecValuePersistentRef : persistentReference,
                kSecReturnAttributes : kCFBooleanTrue
            ]
            var result: AnyObject?

            // Get the current attributes for the item.
            status = SecItemCopyMatching(query, &result)

            if let attributes = result as? [NSObject: AnyObject] where status == errSecSuccess {
                // Update the attributes with the new data.
                var updateQuery = [NSObject: AnyObject]()
                updateQuery[kSecClass] = kSecClassGenericPassword
                updateQuery[kSecAttrService] = attributes[kSecAttrService]

                var newAttributes = attributes
                newAttributes[kSecValueData] = passwordData

                status = SecItemUpdate(updateQuery, newAttributes)
                if status == errSecSuccess {
                    return persistentReference
                }
            }
        }

func getPasswordWithPersistentReference(persistentReference: NSData) -> String? {
        var result: String?
        let query: [NSObject: AnyObject] = [
            kSecClass : kSecClassGenericPassword,
            kSecReturnData : kCFBooleanTrue,
            kSecValuePersistentRef : persistentReference
        ]

        var returnValue: AnyObject?
        let status = SecItemCopyMatching(query, &returnValue)

        if let passwordData = returnValue as? NSData where status == errSecSuccess {
            result = NSString(data: passwordData, encoding: NSUTF8StringEncoding) as? String
        }
        return result
    }