Editing SPFieldMultiColumn and saving updated value

Question

I can get a reference to my SPFieldMultiColumn

 var documentLinkFieldValue = listItems[i]["DocumentLink"] as SPFieldMultiColumnValue;
 var oField = listItems[i].Fields["Document Link"] as SPFieldMultiColumn;

I am making a change to the field value but I am struggling to update the field with the new value

                              if (documentLinkFieldValue != null)
                              {
                                  var link = documentLinkFieldValue[1].Replace("##", "&");
                                  NameValueCollection nvc = HttpUtility.ParseQueryString(link);
                                  if (nvc.Count >= 3)
                                  {
                                      var server = nvc[0] as string;
                                      var db = nvc[1] as string;
                                      var docNum = nvc[2] as string;

                                      var newLink = GetIwsLink(server, db, docNum);

   // Value does not get updated
                                      documentLinkFieldValue[1] = newLink;


                                      listItems[i]["DocumentLink"] = documentLinkFieldValue;
                                      listItems[i].SystemUpdate();
                                  }
                              }

How can I save the value back to the list item?

Answer 1

I have found that this code allows me to update

 oField.ParseAndSetValue(listItems[i], documentLinkFieldValue.ToString());