Question

Basically I have the xml file format likes:

<?xml version="1.0" encoding="utf-8" ?>
<retentions>
   <client id="1544">
      <facility id="5436">
         <retention period="23" />
      </facility>
   </client>
   <client id="7353">
      <facility id="3450">
        <retention period="3" />
     </facility>
   </client>
</retentions>

I want to get all values of all attributes such as “1554”, “5436”, “23” etc.

Please use XDocument instead of XMLDocument.
My code is wrong:

XDocument XDoc = XDocument.Load("my.xml");
   IEnumerable<XElement> results = (from el in XDoc.Root.Elements("retentions")
                                         select el);

UPDATE:(Using dictionary)

var g = from element in XDoc.Descendants("client")
                from ID in element.Attributes("id")
                from Facility in element.Attributes("facility")
                from Period in element.Attributes("period")
                select new { Key = ID.Value, Value = Period.Value };

Answer 1

One line to get all attributes from xml document:

var attributes = ((IEnumerable)xdoc.XPathEvaluate("//@*"))
                      .Cast<XAttribute>().Select(a => (string)a);

UPDATE (dictionary of all nodes attributes)

var attributes = xdoc.Descendants()
                    .GroupBy(e => e.Name)
                    .ToDictionary(g => g.Key.LocalName,
                                  g => g.SelectMany(x => x.Attributes())
                                        .Select(a => (string)a)
                                        .ToList());

List<string> attributesOfClient = attributes["client"];