In that case subscribe to the FieldLayoutInitialized event and write appropriate code logic.
I just wrote this code:
private void XamDataGrid_FieldLayoutInitialized_1(object sender, Infragistics.Windows.DataPresenter.Events.FieldLayoutInitializedEventArgs e)
{
var comboGenderField = e.FieldLayout.Fields["Gender"];
if (comboGenderField != null)
{
var xamComboEditorStyle = new Style(typeof(XamComboEditor));
var itemsProviderSetter = new Setter(XamComboEditor.ItemsProviderProperty,
this.FindResource("cmbGenderProvider"));
xamComboEditorStyle.Setters.Add(itemsProviderSetter);
comboGenderField.Settings.EditorStyle = xamComboEditorStyle;
comboGenderField.Settings.EditAsType = typeof (int);
}
}
Refer this for more info: http://help.infragistics.com/Help/NetAdvantage/WPF/2012.2/CLR4.0/html/xamComboEditor_Setting_the_xamComboEditor_as_an_Editor_of_a_Field_Programmatically.html