WPF ComboBox清楚

EmployeeTypes _ET = new EmployeeTypes();
DataRowCollection drc = _ET.EmpTypeTable.Rows;
foreach (DataRow r in drc)
{
    ComboBoxItem item = new ComboBoxItem();
    item.Tag = r["EmpTypeID"];
    item.Content = r["EmpTypeName"];

    cmbEmpType.Items.Add(item);

    if (cmbEmpType.Items.Count > 0)
    {
        cmbEmpType.SelectedIndex = 0;
    }

}

cmbEmpType.Items.Clear();

cmbEmpType.Items.Clear();