private void AddNewRowToGrid()

    {

        int rowIndex = 0;

        if (ViewState["CurrentTable"] != null)

        {

            DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];

            DataRow drCurrentRow = null;

            if (dtCurrentTable.Rows.Count > 0)

            {

                for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)

                {

                    //extract the TextBox values

                    TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");

                    TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");

                    TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");

                    drCurrentRow = dtCurrentTable.NewRow();

                    drCurrentRow["RowNumber"] = i + 1;

                    dtCurrentTable.Rows[i - 1]["Column1"] = box1.Text;

                    dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;

                    dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;

                    rowIndex++;

                }

                dtCurrentTable.Rows.Add(drCurrentRow);

                ViewState["CurrentTable"] = dtCurrentTable;

                Gridview1.DataSource = dtCurrentTable;

                Gridview1.DataBind();

            }

        }

        else

        {

            Response.Write("ViewState is null");

        }

        //Set Previous Data on Postbacks

        SetPreviousData();

    }

    private void SetPreviousData()

    {

        int rowIndex = 0;

        if (ViewState["CurrentTable"] != null)

        {

            DataTable dt = (DataTable)ViewState["CurrentTable"];

            if (dt.Rows.Count > 0)

            {

                for (int i = 0; i < dt.Rows.Count; i++)

                {

                    TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");

                    TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");

                    TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");

                    box1.Text = dt.Rows[i]["Column1"].ToString();

                    box2.Text = dt.Rows[i]["Column2"].ToString();

                    box3.Text = dt.Rows[i]["Column3"].ToString();

                    rowIndex++;

                }

            }

        }

    }