BindingSource bs = new BindingSource();

        DataTable table = new DataTable();

            table.Columns.Add("Name", typeof(string));

            table.Columns.Add("Value", typeof(int));

            table.Rows.Add("A", );

            table.Rows.Add("B", );

            //comboBox1.DataSource = table;

            //comboBox1.DisplayMember = "Name";

            //comboBox1.ValueMember = "Value";

            ////comboBox1.DataBindings.Add();

            //comboBox1.SelectedIndex = -1;

            bs = new BindingSource();

            bs.DataSource = table;

            bindingNavigator1.BindingSource = bs;

            textBox1.DataBindings.Add(new Binding("Text", bs, "Name"));                

private void bindingNavigatorAddNewItem_Click(object sender, EventArgs e)

        {

            DataRowView row = (DataRowView)bs.Current;

            row["Name"] = "C";

            row["Value"] = ;

            //row.IsNew is true;

            int i = table.Rows.Count;  // = 2

            bs.EndEdit(); //commit to datatable => dataSource get updated

            i = table.Rows.Count; // = 3

            if (row.IsNew) //false

            {

                MessageBox.Show("new row");

            }

        }