Gridview Row -FindControl() not returning value

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"
	            onrowcancelingedit="GridView1_RowCancelingEdit"
	            onrowdeleting="GridView1_RowDeleting" onrowediting="GridView1_RowEditing"
	            onrowupdating="GridView1_RowUpdating">
	        <columns>
	        <asp:TemplateField HeaderText="ProductId">
	        <itemtemplate>
	        <asp:Label ID="lblProductId" runat="server" Text='<%#Eval("ProductId") %>'>'> 
	        </itemtemplate>
	        
	         <asp:TemplateField HeaderText="ProductCategory">
	        <itemtemplate>
	        <asp:Label ID="lblProductCategory" runat="server" Text='<%#Eval("ProductCategory") %>'>'> 
	        </itemtemplate>
	        <edititemtemplate>
	        <asp:TextBox ID="txtProductCategory" runat="server" Text='<%#Eval("ProductCategory") %>'>' >
	        </edititemtemplate>
            
	         <asp:TemplateField HeaderText="GirthFrom">
	        <itemtemplate>
	        <asp:Label ID="lblGirthFrom" runat="server" Text='<%#Eval("GirthFrom") %>'>'> 
	        </itemtemplate>
	        <edititemtemplate>
	        <asp:TextBox ID="txtGirthFrom" runat="server" Text='<%#Eval("GirthFrom") %>'>' >
	        </edititemtemplate>
	        
             <asp:TemplateField HeaderText="GirthTo">
	        <itemtemplate>
	        <asp:Label ID="lblGirthTo" runat="server" Text='<%#Eval("GirthTo") %>'>'> 
	        </itemtemplate>
	        <edititemtemplate>
	        <asp:TextBox ID="txtGirthTo" runat="server" Text='<%#Eval("GirthTo") %>'>' >
	        </edititemtemplate>
	        
	            <asp:TemplateField HeaderText="Action">
                    <itemtemplate>
                        <asp:LinkButton ID="edit" runat="server" CommandName="Edit" Text="Edit">
                        <asp:LinkButton ID="Delete" runat="server" CommandName="Delete" Text="Delete">
                    </itemtemplate>
                    <edititemtemplate>
                        <asp:LinkButton ID="Update" runat="server" CommandName="Update" Text="Update">
                        <asp:LinkButton ID="Cancel" runat="server" CommandName="Cancel" Text="cancel">
                    </edititemtemplate>
                
	        </columns>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
 
public partial class _Default : System.Web.UI.Page
{
    Creation obj=new Creation();
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
 
            Gridviewdatabind();
        }
            
        
    }
    private void Gridviewdatabind()
    {
        DataTable dt = obj.display1();
            GridView1.DataSource = dt;
            GridView1.DataBind();
    }
 
    protected void GridView1_RowDeleting(object sender, GridViewDeleteEventArgs e)
    {
        string lblProductId = ((Label)GridView1.Rows[e.RowIndex].FindControl("lblProductId")).Text;
        obj.ProductId = Convert.ToInt32(lblProductId);
        int res = obj.delete();
        Gridviewdatabind();
        
        
    }
    protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
    {
        GridView1.EditIndex = e.NewEditIndex;
        Gridviewdatabind();
    }
    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {
        string lblProductId = ((Label)GridView1.Rows[e.RowIndex].FindControl("lblProductId")).Text;
 
        string txtProductCategory = ((TextBox)GridView1.Rows[e.RowIndex]
                           .FindControl("txtProductCategory")).Text;
        string txtGirthFrom = ((TextBox)GridView1.Rows[e.RowIndex]
                           .FindControl("txtGirthFrom")).Text;
        string txtGirthTo = ((TextBox)GridView1.Rows[e.RowIndex]
                               .FindControl("txtGirthTo")).Text;
        obj.ProductCategory = txtProductCategory;
        obj.GirthFrom = Convert.ToInt32(txtGirthFrom);
        obj.GirthTo = Convert.ToInt32(txtGirthTo);
        obj.ProductId = Convert.ToInt32(lblProductId);
        int res = obj.update();
        GridView1.EditIndex = -1;
        Gridviewdatabind();
 
    }
    protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
    {
        GridView1.EditIndex = -1;
        Gridviewdatabind();
    }
    
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;
using System.Data.SqlClient;

/// <summary>
/// Summary description for DBoperations
/// </summary>
public class DBoperations
{
    SqlConnection con = new SqlConnection("Data Source=.;Initial Catalog=Micro;Integrated Security=True");
    SqlCommand cmd = null;
	public DBoperations()
	{
		//
		// TODO: Add constructor logic here
		//
	}

public int UPDATECATEGORY(Categorycreation obj)
    {
        cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.CommandText = "SP_Updatecategory";
        cmd.Parameters.AddWithValue("@pdtctg", obj.ProductCategory);
        cmd.Parameters.AddWithValue("@girfrom", obj.GirthFrom);
        cmd.Parameters.AddWithValue("@girto", obj.GirthTo);
        cmd.Parameters.AddWithValue("@pdtid", obj.ProductId);
        con.Open();
        int res = cmd.ExecuteNonQuery();
        con.Close();
        return res;
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;

/// <summary>
/// Summary description for Categorycreation
/// </summary>
public class Categorycreation
{
    DBoperations dbo = new DBoperations();
    public int _Pdtid;
    public string _Pdtctg;
    public int _girfrom;
    public int _girto;
    public int ProductId
    {
        get
        {
            return _Pdtid;
        }
        set
        {
            _Pdtid = value;
        }
    }
    public string ProductCategory
    {
        get
        {
            return _Pdtctg;
        }
        set
        {
            _Pdtctg = value;
        }
    }
    public int GirthFrom
    {
        get
        {
            return _girfrom;
        }
        set
        {
            _girfrom = value;
        }
    }
    public int GirthTo
    {
        get
        {
            return _girto;
        }
        set
        {
            _girto = value;
        }
    }
    public Categorycreation()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    public int update()
    {
        int res = dbo.UPDATECATEGORY(this);
        return res;
    }
}

ALTER PROCEDURE SP_Updatecategory(@pdtctg nvarchar(50),@girfrom int,@girto int,@pdtid int)

AS
BEGIN
update Category set ProductCategory=@pdtctg,GirthFrom=@girfrom,GirthTo=@girto where ProductId=@pdtid
    END

string txtProductCategory = ((TextBox)GridView1.Rows[e.RowIndex]
                           .FindControl("txtProductCategory")).Text;
        string txtGirthFrom = ((TextBox)GridView1.Rows[e.RowIndex]
                           .FindControl("txtGirthFrom")).Text;
        string txtGirthTo = ((TextBox)GridView1.Rows[e.RowIndex]
                               .FindControl("txtGirthTo")).Text;