/// <summary>
/// Evaluates an XPath expression against an XContainer (which is an XElement and an XDocument)
/// and returns an sequence of strings the expression resulted in.
/// It is recommended to pass an XDocument, but if an XElement is submitted, it will be parsed to
/// an XDocument so the XPath expression evaluates as expected.
/// </summary>
/// <param name="xContainer">
/// The XElement or XDocument the XPath will be applied to.
/// NOTE: if an XElement is submitted, it will be parsed into an XDocument before the XPath expression is evaluated.
/// </param>
/// <param name="xPath">A string containing the XPath expression to evaluate with.</param>
/// <param name="exceptionMessage">The exception message string.</param>
/// <returns>
/// Returns an IEnumerable of strings containing all resulting element and attribute values evaluated with the XPath
/// expression.
/// If nothing was found, then an empty enumerable is returned.
/// </returns>
public static IEnumerable <string> SelectXPathValues(this XContainer xContainer, string xPath,
out string exceptionMessage)
{
exceptionMessage = string.Empty;
if (xContainer == null || xPath.HasNoValue())
{
return(Enumerable.Empty <string>());
}
var errorSb = new Lazy <StringBuilder>();
var results = Enumerable.Empty <string>();
if (xPath.HasNoValue())
{
return(results);
}
// if the container is an element, parse it to a document so the xpath evaluation works as expected.
if (xContainer is XElement)
{
xContainer = XDocument.Parse(xContainer.ToString());
}
var manager = new XmlNamespaceManager(xContainer.CreateNavigator().NameTable);
IEnumerable <object> xObjects;
object xDocXPathEvaluate;
try
{
xDocXPathEvaluate = xContainer.XPathEvaluate(xPath, manager);
}
catch (Exception ex)
{
var xmlMessage = new XElement("exception", new XElement("xPath", xPath),
new XElement("message", ex.Message));
errorSb.Value.AppendFormat("Error Evaluating XPath: {0}. ", xmlMessage);
return(results);
}
var xDocXPathEvaluateAsIEnumerable = xDocXPathEvaluate as IEnumerable <object>;
if (xDocXPathEvaluateAsIEnumerable != null)
{
xObjects = xDocXPathEvaluateAsIEnumerable;
}
else
{
return new List <string> {
xDocXPathEvaluate.ToString()
}
};
if (xObjects.NoItems())
{
errorSb.Value.AppendFormat("Xpath did not find results: {0}", xPath);
}
// return the evaluated strings
results = (from e in xObjects.OfType <XElement>()
select(string) e)
.Concat(
from e in xObjects.OfType <XAttribute>()
select(string) e);
if (errorSb.IsValueCreated)
{
exceptionMessage = errorSb.Value.ToString();
}
return(results);
}