Regex Validation for TreelistEx is not working - regex

Question

In Sitecore Content editor/Page editor, when I add items to TreelistEx I would like the TreelistEx to allow only 12 items. To achieve this solution, I have added a Regex ^.{0,467}$ in the validation field inside the template section in which I want to limit the items.
I have referred this article
This Regex works properly in Content editor. But for the page editor whenever I add an items in treelistEx it works fine for the first time but again if I add/remove items it gives me validation message for both greater and less number of items just after on click of "Ok"and items are also not saved.
Ideally it should give validation message if number of items are greater than 12 and only on Click of "save" button same as it is working in Content editor. How can I solve this Regex validation problem in Page editor? I am using Sitecore 8.1

Answer 1

I also had the same issue a while ago and because of the limited time i had i implemented a not so ideal way but you can implement it if you want.
Let the user add the items and then just grab the first 12 in your code. It will be something like this:
Create a method to get the multicast item (For flexibility).
public static MultilistField GetMultilistField(Item item, string fieldName)
{
if (item != null && !string.IsNullOrWhiteSpace(fieldName))
{
MultilistField field = item.Fields[fieldName];
if (field != null)
{
return field;
}
}
return null;
}
Get the items within the Miltilist field.
MultilistField field = GetMultilistField[DatasourceItem, "fieldName"];
var returnList = field.GetItems().Where(c => c.TemplateName.Equals("someValidationIfYouWant")).ToList().Take(12);