Gridview data is not getting updated

<asp:GridView ID="gvcategory" runat="server" AutoGenerateColumns="False" OnPageIndexChanging="gvcategory_PageIndexChanging"
OnRowCancelingEdit="gvcategory_RowCancelingEdit" OnRowDeleting="gvcategory_RowDeleting" OnRowEditing="gvcategory_RowEditing"
OnRowUpdating="gvcategory_RowUpdating" BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px"
CellPadding="3" GridLines="Vertical" AllowPaging="True" Width="50%" >
  <asp:TemplateField HeaderText="category id">
  <asp:Label ID="lblcatid" runat="server" Text='<%#Eval("category_id") %>'>
  <asp:TemplateField HeaderText="category name">
  <asp:TextBox ID="txtcategory" runat="server" Text='<%#Eval("category_name") %>'>
  <asp:TemplateField>
  <asp:LinkButton ID="lnkbtnUpdate" CausesValidation="true" CommandName="update" runat="server" Text="update">
  <asp:LinkButton ID="lnkbtnCancel" runat="server" Text="cancel" CommandName="cancel" CausesValidation="true">
  <asp:LinkButton ID="lnkEdit" runat="server" CausesValidation="true" CommandName="edit" Text="edit">
   <asp:CommandField ShowDeleteButton="True" />
  <SelectedRowStyle BackColor="#008A8C" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#000084" Font-Bold="True" ForeColor="White" />

Imports System.Data.SqlClient
Imports System.Data
Partial Class management_add_category
    Inherits System.Web.UI.Page
    Dim obj As New data
    Dim da As SqlDataAdapter
    Dim ds As DataSet
    Protected Sub btnadd_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnadd.Click
        obj.Connect()
        obj.cmd.CommandText = "insert into category_master(category_name)values('" & txtcategory.Text & "')"
        obj.cmd.ExecuteNonQuery()
        MsgBox("category added!", MsgBoxStyle.Information, "Mohire`s")
        txtcategory.Text = ""
        obj.db.Close()
        fill_data()
    End Sub

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Session("user_id") = "" Then
            Response.Redirect("admin_login.aspx")
        End If
        fill_data()
    End Sub

    Private Sub fill_data()

        obj.Connect()
        obj.cmd.CommandText = "Select * from category_master order by category_id asc"
        da = New SqlDataAdapter(obj.cmd)
        ds = New DataSet
        da.Fill(ds, "category_master")
        gvcategory.DataSource = ds.Tables("category_master")
        gvcategory.DataBind()
        obj.db.Close()

    End Sub

    Protected Sub gvcategory_PageIndexChanging(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewPageEventArgs) Handles gvcategory.PageIndexChanging
        gvcategory.PageIndex = e.NewPageIndex
        fill_data()
    End Sub

    Protected Sub gvcategory_RowCancelingEdit(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewCancelEditEventArgs) Handles gvcategory.RowCancelingEdit
        gvcategory.EditIndex = -1
        fill_data()
    End Sub

    Protected Sub gvcategory_RowDeleting(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewDeleteEventArgs) Handles gvcategory.RowDeleting
        Dim l1 As Label = CType(gvcategory.Rows(e.RowIndex).FindControl("lblcatid"), Label)
        obj.Connect()
        obj.cmd.CommandText = "delete category_master where category_id=" & l1.Text & ""
        obj.cmd.ExecuteNonQuery()
        gvcategory.EditIndex = -1
        MsgBox("category deleted!", MsgBoxStyle.Information, "Mohire`s")
        obj.db.Close()

        fill_data()

    End Sub

    Protected Sub gvcategory_RowEditing(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewEditEventArgs) Handles gvcategory.RowEditing
        gvcategory.EditIndex = e.NewEditIndex
        fill_data()
    End Sub

    Protected Sub gvcategory_RowUpdating(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.GridViewUpdateEventArgs) Handles gvcategory.RowUpdating
        Try
            Dim l1 As Label = CType(gvcategory.Rows(e.RowIndex).FindControl("lblcatid"), Label)
            Dim txtcatname As TextBox = CType(gvcategory.Rows(e.RowIndex).FindControl("txtcategory"), TextBox)

            obj.Connect()
            obj.cmd.CommandText = "update category_master set category_name='" & txtcatname.Text & "' where category_id=" & l1.Text
            obj.cmd.ExecuteNonQuery()
            gvcategory.EditIndex = -1
            MsgBox("category updated!", MsgBoxStyle.Information, "Mohire`s")
            obj.db.Close()

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
        fill_data()
    End Sub
End Class