C#

string path = Properties.Settings.Default.XMLFolder + list + ".xml";
            XmlTextReader rdr = new XmlTextReader(path);
            XmlDocument doc = new XmlDocument();
            doc.Load(rdr);
 XmlNode nodeBusiness = doc.CreateNode(XmlNodeType.Element, "Business", string.Empty);
            nodeBusiness.Attributes.Append(attribute);
            docData.AppendChild(nodeBusiness);

//Lists as properties
List<RCH.EL.EMR.Allergies> AllAllergies
{ get; set; }

List<RCH.EL.EMR.Allergies> RemainingAllergies
{ get; set; }

List<RCH.EL.EMR.Allergies> PatientAllergies
{ get; set; }

//Method that seperates the items in the lists
private void ResolveAllergies()
{
    RemainingAllergies = AllAllergies.Except(PatientAllergies).ToList();
}

//Method that binds
protected override void BindListBoxes()
{
    lstAllergies.DataSource = RemainingAllergies;
    lstAllergies.DisplayMember = "AllergyAr";
    lstAllergies.ValueMember = "ID";

    lstPatientAllergies.DataSource = PatientAllergies;
    lstPatientAllergies.DisplayMember = "AllergyAr";
    lstPatientAllergies.ValueMember = "ID";
}

//event handler methods that move the items from one list to the other (arrow buttons on the form)
private void btnAddLeft_Click(object sender, EventArgs e)
{
    
    PatientAllergies.Add((RCH.EL.EMR.Allergies)lstAllergies.SelectedItem);
    ResolveAllergies();
    lstAllergies.Refresh();
    lstPatientAllergies.Refresh();
    BindListBoxes();
}

private void btnAddRight_Click(object sender, EventArgs e)
{

    PatientAllergies.Remove((RCH.EL.EMR.Allergies)lstAllergies.SelectedItem);
    ResolveAllergies();
    lstAllergies.Refresh();
    lstPatientAllergies.Refresh();
    BindListBoxes();
}