Find the sum of all values of a column in ListView

Question

In my ListView, I have InsertTemplate : 

            <InsertItemTemplate>

<td>

<asp:DynamicControl runat="server" DataField="PercentageOfPayment" ID="PercentageOfPaymentIns" Mode="Insert" />

</td>

            </InsertItemTemplate>

In my InsertMethod, I want to iterate thru all the items of ListView & sum up the values of "PercentageOfPayment" field. If it exceeds 100, I want to warn the user. This is the code of my InsertMethod that shows various things I had tried for this :

        public void paymentList_InsertItem()

        {

            decimal percentagetotal = 0;

            if (currentProject == null)

                currentProject = _db.Projects.Find(projectId);

            var item = new VincitoreCRMApplication.Models.PaymentSchedule(projectId, projectName);

            TryUpdateModel(item);

            if (ModelState.IsValid)

            {

                              

                foreach (ListViewItem lvi in paymentList.Items)

                {

                    PaymentSchedule sc = (PaymentSchedule)lvi.DataItem;

                    if (sc != null)

                    {

                        System.Diagnostics.Debug.WriteLine("$$$$$$$$$ SC = " + sc.PercentageOfPayment);

                    }

                    else

                        System.Diagnostics.Debug.WriteLine("$$$$$$$$$ SC = null");

                    /*

                    //if (Decimal.TryParse(lvi.))

                    if (lvi.ItemType == ListViewItemType.DataItem)

                    {

                        System.Web.DynamicData.DynamicControl dc = paymentList.FindControl("PercentageOfPaymentIns") as System.Web.DynamicData.DynamicControl;

                        

                    }

                    percentagetotal += p.PercentageOfPayment;*/

                } 

                //paymentList.Items.Sum()

                if ((totalPercentage + item.PercentageOfPayment) > 100)

                {

                    System.Diagnostics.Debug.WriteLine("$$$$$$$$$ PERCENTAGE TOTAL Comes To " + percentagetotal + " .. NOT Valid > 100");

                }

                else

                {

                    // Save changes here

                    _db.PaymentScheduleOfProject.Add(item);

                    _db.SaveChanges();

                    paymentList.EditIndex = -1;

                }

            }

        }

I referred many sites, tried to iterate and find the sum, but couldn't achieve it. What am I missing over here, can you point out and help me solve it !! 

Any help is highly appreciated.

Thanks