Adding Dynamic Rows in GridView with TextBoxes in Asp.Net with C#

Step 1 : Copy and Past below code on  Default.aspx page

        <asp:GridView ID="Gridview1" runat="server" ShowFooter="true"

            AutoGenerateColumns="false">

            <Columns>

                <asp:BoundField DataField="RowNumber" HeaderText="Row Number" />

                <asp:TemplateField HeaderText="Header 1">

                    <ItemTemplate>

                        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>

                    </ItemTemplate>

                </asp:TemplateField>

                <asp:TemplateField HeaderText="Header 2">

                    <ItemTemplate>

                        <asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>

                    </ItemTemplate>

                </asp:TemplateField>

                <asp:TemplateField HeaderText="Header 3">

                    <ItemTemplate>

                        <asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>

                    </ItemTemplate>

                    <FooterStyle HorizontalAlign="Right" />

                    <FooterTemplate>

                        <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" />

                    </FooterTemplate>

                </asp:TemplateField>

            </Columns>

        </asp:GridView>

Step 2 : Copy and Past below code on  Default.aspx.cs page

    protected void Page_Load(object sender, EventArgs e)

    {

        if (!Page.IsPostBack)

        {

            SetInitialRow();

        }

    }

    private void SetInitialRow()

    {

        DataTable dt = new DataTable();

        DataRow dr = null;

        dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));

        dt.Columns.Add(new DataColumn("Column1", typeof(string)));

        dt.Columns.Add(new DataColumn("Column2", typeof(string)));

        dt.Columns.Add(new DataColumn("Column3", typeof(string)));

        dr = dt.NewRow();

        dr["RowNumber"] = 1;

        dr["Column1"] = string.Empty;

        dr["Column2"] = string.Empty;

        dr["Column3"] = string.Empty;

        dt.Rows.Add(dr);

        //Store the DataTable in ViewState

        ViewState["CurrentTable"] = dt;

        Gridview1.DataSource = dt;

        Gridview1.DataBind();

    }

    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;

                    drCurrentRow["Column1"] = box1.Text;

                    drCurrentRow["Column2"] = box2.Text;

                    drCurrentRow["Column3"] = box3.Text;

                    rowIndex++;

                }

                //add new row to DataTable

                dtCurrentTable.Rows.Add(drCurrentRow);

                //Store the current data to ViewState

                ViewState["CurrentTable"] = dtCurrentTable;

                //Rebind the Grid with the current data

                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 = 1; 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++;

                }

            }

        }

    }

    protected void ButtonAdd_Click(object sender, EventArgs e)

    {

        AddNewRowToGrid();

    }