title: ObservableCollection and IDataErrorInfo with a XML file
body: <p>MainWindow() and GetXmlData() work fine and display the xmlfile on gridview. But when I include the XmlNode :IDataErrorInfo class, it stops working. </p>
  
  <p>I like to get all of them to work to display and validate the gridview. Anyone could spot anything I miss? Or explanation, I'm hitting a stop here. It seems like an error between observablecollection.</p>
  
  <pre><code>    public MainWindow()
      {
          InitializeComponent();
          RadGridView testGrid = new RadGridView();
          testGrid.ItemsSource = GetXmlData();
          testGrid.AutoGenerateColumns = false;
          GridViewDataColumn col1 = new GridViewDataColumn();
          col1.DataMemberBinding = new Binding("JobKey") { 
          ValidatesOnDataErrors = true, NotifyOnValidationError = true };                      
          testGrid.Columns.Add(col1);
          LayoutRoot.Children.Add(testGrid);                 
     }
  
      private static object GetXmlData()
      {
          XmlDocument doc = new XmlDocument();
          doc.Load(@"c:\\JobSetupFile.xml");
  
          XmlDataProvider provider = new XmlDataProvider();
          provider.IsAsynchronous = false;
          provider.Document = doc;
          provider.XPath = "JobSetup/JobParameters";
  
          return new ObservableCollection&lt;XmlNode&gt;((IEnumerable&lt;XmlNode&gt;)provider.Data);
      }
  
      public class XmlNode : IDataErrorInfo
      {
          public string JobKey { get; set; }
  
          public XmlNode()
          {
  
          }
  
          public string Error
          {
              get { throw new NotImplementedException(); }
          }
  
          public string this[string columnName]
          {
              get
              {
                  string result = string.Empty;
                  if (columnName.Equals("JobKey"))
                  {
                      if (JobKey.Where(s =&gt; Char.IsLetter(s)).Count() != JobKey.Length)
                          result = "Invalid name format. Name should contain letters only";
                  }
               return result;
              }
          }
      }
  </code></pre>