"SharePoint list itme update error : Invalid data has been used to update the list item. The field you are trying to update may be read only."

Question

Hi Everyone,
i am facing one problem ...
when i am updating an SharePoint List item, it is throwing above error....
This is my code......
 try
                tbl = getListDateTable("NCR");
                DataTable dt = tbl;
                oWebsite = mysite.OpenWeb();
                oList = oWebsite.Lists["NCR"];
                SPListItem itemToUpdate = null;
                foreach (SPListItem listItem in oList.Items)
                    listItem.Update();
                    workOrderID = Convert.ToInt32(txtTitle.Text);
                    itemToUpdate = listItem;
                //SPListItem itemToUpdate = oList.GetItemById(workOrderID);
                //itemToUpdate.Fields["Title"].ReadOnlyField = false;
                //string str = ddlStatus.SelectedValue;
                itemToUpdate["Title"] = txtTitle.Text;
                itemToUpdate["JobNumber"] = txtJobNumber.Text;
                itemToUpdate["PartNumber"] = txtPartNumber.Text;
                itemToUpdate["PartDescription"] = txtPartDescription.Text;
                //itemToUpdate["RequiredBy"] = txtRequiredBy.Text;
                itemToUpdate["ReportedBy"] = txtReportedBy.Text;
                itemToUpdate["WrittenBy"] = txtWrittenBy.Text;
                //itemToUpdate["DateOpened"] = txtDateOpened.SelectedDate;
                //itemToUpdate["DateClosed"] = txtDateClosed.SelectedDate;
                itemToUpdate.Update();
                oList.Update();
               // bind();
            catch (Exception ex)
                throw ex;
Thanks
viswanath

Answer 1

Hi Viswanath,
If you are using People/User Type Field Column then use below code methord
SPUser user = web.EnsureUser(loginName);
item["UserTypeFieldName"] = user;
Lookup Type Field Column then use below code methord
public static SPFieldLookupValue GetLookupFieldFromValue(string lookupValue,string lookupSourceColumn, SPList lookupSourceList)
SPFieldLookupValue value = null;
SPQuery query = new SPQuery();
query.Query = "<Where><Eq><FieldRef Name='" + lookupSourceColumn + "'/><Value Type='Text'>" + lookupValue + "</Value></Eq></Where>";
SPListItemCollection listItems = lookupSourceList.GetItems(query);
if(listItems.Count > 0 )
value = new SPFieldLookupValue(listItems[0].ID,lookupValue);
return value;
item["LookupField"] = GetLookupFieldFromValue(lookupfieldValue, lookupSourceColumn, listName);
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