Retain dynamic controls value when adding new row in GridView using C# in ASP.Net

Hi jochk12345,

Refer below modified code.

HTML

<asp:GridView ID="Gridview1" runat="server" ShowFooter="True" AutoGenerateColumns="False" OnRowDataBound="Gridview1_RowDataBound">
    <Columns>
        <asp:BoundField DataField="RowNumber" HeaderText="Row Number" />
        <asp:TemplateField HeaderText="Header 1">
            <ItemTemplate>
                <asp:Label ID="Label1" runat="server" Text='<%# Bind("Column1") %>' Visible="false"></asp:Label>
                <asp:TextBox ID="TextBox1" runat="server" Visible="true"></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" OnClick="ButtonAdd_Click1" />
            </FooterTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

Namespaces

using System.Data;

Code

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"] = "asp.net";
    dr["Column2"] = string.Empty;
    dr["Column3"] = string.Empty;
    dt.Rows.Add(dr);
    dr = dt.NewRow();
    dr["RowNumber"] = 2;
    dr["Column1"] = "java";
    dr["Column2"] = string.Empty;
    dr["Column3"] = string.Empty;
    dt.Rows.Add(dr);
    dr = dt.NewRow();
    dr["RowNumber"] = 3;
    dr["Column1"] = string.Empty;
    dr["Column2"] = string.Empty;
    dr["Column3"] = string.Empty;
    dt.Rows.Add(dr);
    ViewState["CurrentTable"] = dt;
    Gridview1.DataSource = dt;
    Gridview1.DataBind();
}
private void AddNewRowToGrid()
{
    int rowIndex = 0;
    if (ViewState["CurrentTable"] != null)
    {
        DataTable dt = (DataTable)ViewState["CurrentTable"];

        DataRow dr = null;

        if (dt.Rows.Count > 0)
        {
            for (int i = 1; i <= dt.Rows.Count; i++)
            {
                dr = dt.NewRow();
                dr["RowNumber"] = i + 1;

                if (rowIndex <= 1)
                {
                    Label box1 = (Label)Gridview1.Rows[rowIndex].Cells[1].FindControl("Label1");
                    dt.Rows[i - 1]["Column1"] = box1.Text;
                }
                else
                {
                    TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
                    dt.Rows[i - 1]["Column1"] = box1.Text;
                }

                TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                dt.Rows[i - 1]["Column2"] = box2.Text;
                dt.Rows[i - 1]["Column3"] = box3.Text;
                rowIndex++;
            }
            dt.Rows.Add(dr);
            ViewState["CurrentTable"] = dt;
            Gridview1.DataSource = dt;
            Gridview1.DataBind();
        }
    }
    else
    {
        Response.Write("ViewState is null");
    }
    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++)
            {
                GridViewRow gvrow = Gridview1.Rows[i];
                if (gvrow.RowIndex == 1)
                {
                    Label box1 = (Label)Gridview1.Rows[rowIndex].Cells[1].FindControl("Label1");
                    box1.Text = dt.Rows[i]["Column1"].ToString();
                }
                else
                {
                    TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
                    box1.Text = dt.Rows[i]["Column1"].ToString();
                }

                TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                box2.Text = dt.Rows[i]["Column2"].ToString();
                box3.Text = dt.Rows[i]["Column3"].ToString();
                rowIndex++;
            }
        }
    }
}
protected void ButtonAdd_Click1(object sender, EventArgs e)
{
    AddNewRowToGrid();
}
protected void Gridview1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        int index = e.Row.RowIndex;
        if (Gridview1.Rows.Count == 1)
        {
            TextBox t1 = (TextBox)Gridview1.Rows[0].FindControl("TextBox1");
            Label l1 = (Label)Gridview1.Rows[0].FindControl("Label1");
            t1.Visible = false;
            l1.Visible = true;
        }
        if (Gridview1.Rows.Count == 2)
        {
            TextBox t1 = (TextBox)Gridview1.Rows[1].FindControl("TextBox1");
            Label l1 = (Label)Gridview1.Rows[1].FindControl("Label1");
            t1.Visible = false;
            l1.Visible = true;
        }
    }
}