private List<Item> items = new List<Item>();

  private void _LoadItems() {
            Order order = _GetOrder();
            if (order == null)
                return;
            using (SqlConnection connection = new SqlConnection(Properties.Settings.Default.ConnectionString)) {
                connection.Open();
                var command = new SqlCommand("SelectItems", connection);
                command.CommandType = System.Data.CommandType.StoredProcedure;
                command.Parameters.AddWithValue("@OrderNumber", order.OrderNumber);
                var adapter = new SqlDataAdapter(command);
                var table = new DataTable();
                adapter.Fill(table);
                this.items.Clear();
                foreach (DataRow row in table.Rows) {
                    var item = new Item(row);
                    this.items.Add(item);
                }
                this.lvItems.ItemsSource = this.items;
                MessageBox.Show(this.items.Count + "");
            }
        }

<ListView Margin="0" Name="lvItems" SelectionChanged="lvItems_SelectionChanged">
                    <ListView.View>
                        <GridView>
                            <GridViewColumn Header="Description" Width="400" DisplayMemberBinding="{Binding Description}" />
                            <GridViewColumn Header="Unit Price" Width="150" DisplayMemberBinding="{Binding UnitPrice}" />
                            <GridViewColumn Header="Quantity" Width="150" DisplayMemberBinding="{Binding Quantity}" />
                        </GridView>
                    </ListView.View>
                </ListView>