how adding rows to grid view after selecting drop down list

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C#

ASP.NET

I have read article Dynamically adding and deleting rows from ASP.NET Grid View (http://www.codeproject.com/Articles/467788/Dynamically-adding-and-deleting-rows-from-ASP-NET)
- in this article we add rows manually and always we have 1 empty row for filling, now i like to change code a bit:
1- remove empty row from end of gridview
2- after selecting value from drop down list we add rows to grid view.
the code for addnewrow in the article is like below:

private void AddNewRow()
{
    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++)
            {
                TextBox TextBoxName =
                  (TextBox)grvStudentDetails.Rows[rowIndex].Cells[1].FindControl("txtName");
                TextBox TextBoxAge =
                  (TextBox)grvStudentDetails.Rows[rowIndex].Cells[2].FindControl("txtAge");
                TextBox TextBoxAddress =
                  (TextBox)grvStudentDetails.Rows[rowIndex].Cells[3].FindControl("txtAddress");
                RadioButtonList RBLGender =
                  (RadioButtonList)grvStudentDetails.Rows[rowIndex].Cells[4].FindControl("RBLGender");
                DropDownList DrpQualification =
                  (DropDownList)grvStudentDetails.Rows[rowIndex].Cells[5].FindControl("drpQualification");
                drCurrentRow = dtCurrentTable.NewRow();
                drCurrentRow["RowNumber"] = i + 1;

                dtCurrentTable.Rows[i - 1]["Col1"] = TextBoxName.Text;
                dtCurrentTable.Rows[i - 1]["Col2"] = TextBoxAge.Text;
                dtCurrentTable.Rows[i - 1]["Col3"] = TextBoxAddress.Text;
                dtCurrentTable.Rows[i - 1]["Col4"] = RBLGender.SelectedValue;
                dtCurrentTable.Rows[i - 1]["Col5"] = DrpQualification.SelectedValue;
                rowIndex++;
            }
            dtCurrentTable.Rows.Add(drCurrentRow);
            ViewState["CurrentTable"] = dtCurrentTable;

            grvStudentDetails.DataSource = dtCurrentTable;
            grvStudentDetails.DataBind();
        }
    }
    else
    {
        Response.Write("ViewState is null");
    }
    SetPreviousData();
}