private void AddColumn_Click(object sender, RoutedEventArgs e)
{
dt.Columns.Add(new DataColumn("New Column" + newColumnIndex++));
for (int i = 0; i < dt.Rows.Count; i++)
{
dt.Rows[i][dt.Columns.Count - 1] = i.ToString() + " - New Column";
}
dataGrid.ItemsSource = null;
dataGrid.ItemsSource = dt.DefaultView;
}