Add field to content type in specific position

Question

THe code below is working perfect, however I need the new field to be in the 5th position, and not at the end in the forms.

Any idea how?

private void UpdateDossierContentType(SPWeb parentWeb)
        {
            #region Adds the product name lookup to the content type Dossier
                SPList productList = parentWeb.Site.RootWeb.Lists["Product"];
                SPFieldLookup lookup = CreateLookupField("ProductNameLookup", "CustomGroup",
                        false, false, parentWeb.Site.RootWeb,
                        parentWeb.Site.RootWeb.Lists["Product"],
                       productList.Fields["Product Name"].InternalName);
               LinkFieldToContentType(parentWeb.Site.RootWeb, "Dossier", (SPField)lookup);
            #endregion

            #region Removes the old product name managed metadata field from the content type.
                //SPContentType dossierCT = productList.ContentTypes["Dossier"];
                //dossierCT.DeleteFieldRefFromContentType(parentWeb.Fields["Product"]);
                //dossierCT.Update();
            #endregion
        }

        public static void LinkFieldToContentType(SPWeb web, string contentType, SPField field)
        {
            SPContentType ct = web.ContentTypes[contentType];
            ct.FieldLinks.Add(new SPFieldLink(field));
            ct.Update(true);
        }

        public static SPFieldLookup CreateLookupField(string fieldName,
     string group, bool required, bool allowMultipleValues, SPWeb w,
     SPList lookupList, string lookupField)
        {
            w.Fields.AddLookup(fieldName, lookupList.ID, lookupList.ParentWeb.Site.RootWeb.ID, required);
            SPFieldLookup lookup = (SPFieldLookup)w.Fields[fieldName];
            lookup.AllowMultipleValues = allowMultipleValues;
            lookup.LookupField = lookupField;
            lookup.Group = group;
            lookup.Update(true);
            return lookup;
        }

Update 1:

 MoveFieldInColumnOrder(parentWeb, "Dossier", productList.Fields["Product Name"].InternalName, 25);

  public static void MoveFieldInColumnOrder(SPWeb web, string contentTypeName, string internalName, int insertAt)
        {
            SPContentType ct = web.Site.RootWeb.ContentTypes[contentTypeName];
            List<string> listOfFieldNames = new List<string>();
            foreach (SPFieldLink fl in ct.FieldLinks)
            {
                listOfFieldNames.Add(fl.Name);
            }
            listOfFieldNames.Remove(internalName);
            listOfFieldNames.Insert(insertAt, internalName);
            ct.FieldLinks.Reorder(listOfFieldNames.ToArray());
            ct.Update(true, true);
        }

Answer 1

There might be more elegant ways of doing this, but the following works for me:

    public static void MoveFieldInColumnOrder(SPList list, SPContentTypeId ctId, string internalName, int insertAt)
    {
        SPContentTypeId ct = list.ContentTypes.BestMatch(ctId);
        SPContentType cType = list.ContentTypes[ct];

        List<string> listOfFieldNames = new List<string>();

        foreach (SPFieldLink fl in cType.FieldLinks)
        {
            listOfFieldNames.Add(fl.Name);
        }

        listOfFieldNames.Remove(internalName);
        listOfFieldNames.Insert(insertAt, internalName);

        cType.FieldLinks.Reorder(listOfFieldNames.ToArray());

        cType.Update(false, true);
    }

Answer 2

You can use SPFieldLinkCollection.Reorder just pass it the internal names of the first 5 fields