Checkbox in datagridview

Protected Sub CheckItem_CheckedChanged(sender As Object, e As EventArgs)
        Dim chkstatus As CheckBox = CType(sender, CheckBox)
        Dim row As GridViewRow = CType(chkstatus.NamingContainer, GridViewRow)
    End Sub

Protected Sub CheckHeader_CheckedChanged(sender As Object, e As EventArgs)
        Dim chckheader As CheckBox = CType(RequestHeader.HeaderRow.FindControl("CheckHeader"), CheckBox)

        For Each row As GridViewRow In RequestHeader.Rows
            Dim chckrw As CheckBox = CType(row.FindControl("CheckItem"), CheckBox)

            If chckheader.Checked = True Then
                chckrw.Checked = True
            Else
                chckrw.Checked = False
            End If
        Next
    End Sub

Protected Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click

        For i As Integer = 0 To RequestHeader.Rows.Count - 1

            Dim chkdelete As CheckBox = CType(RequestHeader.Rows(i).Cells(0).FindControl("CheckItem"), CheckBox)

            If chkdelete.Checked = True Then
                Dim id As Integer = Convert.ToInt32(RequestHeader.Rows(i).Cells(0).Text)

                Using cn As New SqlConnection(System.Web.Configuration.WebConfigurationManager.ConnectionStrings("WFH").ConnectionString)
                    Using cmd As New SqlCommand()
                        cmd.CommandType = CommandType.Text
                        cmd.Connection = cn
                        cn.Open()
                        cmd.CommandText = "UPDATE Approver SET DisApproveDate = @Date  where Request_NO= '" & id & "' "
                        cmd.Parameters.AddWithValue("@Date", SqlDbType.SmallDateTime).Value = DateTime.Now
                        cmd.ExecuteNonQuery()
                        RequestHeader.EditIndex = -1
                        DataBind()
                        cn.Close()
                    End Using
                End Using
            End If
        Next

    End Sub