Question

i am trying to get the Distinct from the XMLDocument and load into the Dropdownlist.

var topicNodes = xdoc.SelectNodes("//content:Topic", nsmgr).Cast<XmlNode>().Select(c =>   c.InnerText).Distinct();  

here is my full code:

    XmlDocument xdoc = new XmlDocument();//xml doc used for xml parsing
    xdoc.Load(url);    
    XmlNamespaceManager nsmgr = new XmlNamespaceManager(xdoc.NameTable);
    nsmgr.AddNamespace("content", "sitename.xsd");

    var topicNodes = xdoc.SelectNodes("//content:Topic", nsmgr).Cast<XmlNode>().Select(c =>   c.InnerText).Distinct();  

    foreach (XmlNode node in topicNodes)
    {
        string topic = node.Attributes["TopicName"].Value;
        //dropdownlist.items.add(new listitem(topic);
        this.dropdownlist.Items.Add(new  ListItem(topic);  
    }
    dropdownlist.databind();

Answer 1

Why don’t you use Linq to XML?

Otherwise create a key value array and use the value to distinct on as key.

Edit:

Your distincting on the InnerText is that the correct value? Try to distinct first and then select the innerText.

Try

var topicNodes = xdoc.SelectNodes("//content:Topic", nsmgr).Cast<XmlNode>()**.Distinct()**.Select(c => c.InnerText).ToList();

Edit2:

Use this method:

public static IEnumerable<TSource> DistinctBy<TSource, TKey>
     (this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    HashSet<TKey> knownKeys = new HashSet<TKey>();
    foreach (TSource element in source)
    {
        if (knownKeys.Add(keySelector(element)))
        {
            yield return element;
        }
    }
}

You have to select on witch field you would like to distinct. The XmlNode with the same ID is not the same object!