1、string => List<long>
string ShopIds = "1,2,3";
var ShopIdList = ShopIds.Split(‘,‘).Select(p => p.ToLong()).ToList()
2、List<long> => string
List<long> = new List<long>{1,2,3};
string ShopIds = string.Join(",", shopSkuIds);
原文：http://www.cnblogs.com/afei9527/p/4775764.html