'System.Xml.XmlException' occurred in System.Xml.dll but was not handled in user code

Question

I have a string like

new_responseString ="<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>\n<lab:lab xmlns:udf=\"http://ghjhjhj.com/ri/userdefined\" xmlns:ri=\"http://kjkj.com/ri\" xmlns:lab=\"http://iuiuu.com/ri/lab\" uri=\"https://hhjjhjhj.org/api/v2/labs/1\">\n    <name>Administrative Lab</name>\n    <billing-address>\n        <street></street>\n        <city></city>\n        <state></state>\n        <country></country>\n        <postalCode></postalCode>\n        <institution></institution>\n        <department></department>\n    </billing-address>\n    <shipping-address>\n        <street></street>\n        <city></city>\n        <state></state>\n        <country></country>\n        <postalCode></postalCode>\n        <institution></institution>\n        <department></department>\n    </shipping-address>\n    <udf:field type=\"String\" name=\"Account ID\">adm</udf:field>\n    <website></website>\n</lab:lab>\n"   

In order to just extract the value adm ie any value between the tag <udf></udf>

var new_response = new_client.GetAsync(new_Uri).Result;
string new_responseString = new_response.Content.ReadAsStringAsync().Result;
var new_doc = XDocument.Parse(new_responseString);
var udf = "http://ghjhjhj.com/ri/userdefined";
var udfValue = doc.Descendants(udf + "field").FirstOrDefault(field => field.Attribute("name").Value.Equals("Account ID")).Value;
return udfValue;

But this throws an exception

System.Xml.XmlException: The ':' character, hexadecimal value 0x3A, cannot be included in a name

I have one more question instead of reading the response as string like ReadAsStringAsync() in string new_responseString = new_response.Content.ReadAsStringAsync().Result can this be retrieved in the original format the API returns the response.

Answer 1

The correct way to use a namespace is with XNamespace :

XNamespace ns = "http://ghjhjhj.com/ri/userdefined";
var udfValue = new_doc.Descendants(ns + "field").FirstOrDefault(field => field.Attribute("name").Value.Equals("Account ID")).Value;