title: WPF validation rule problems in a datagrid
body: <p>I'm having a problem using a validation rule in a data grid:</p>
  
  <p>I want to use a ValidationRule on a DataGridComboBoxColumn, I used <a href="http://msdn.microsoft.com/en-us/library/ee622975.aspx" rel="nofollow">this example</a></p>
  
  <p>for guidance, in particular the BindingGroup stuff.</p>
  
  <p>This works to an extent but seems very broken. The ValidatioRule doesn't fire as soon as the combo box selection changes, instead it fires only when I change the selection then click on another row in the DataGrid. I really need it to fire as soon as I have changed the selection of the combo box.</p>
  
  <p>I've tried messing with the validation step but to no avail, can anybody help?</p>
  
  <p>Thanks in advance!</p>