using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

​

namespace ConsoleApplication10 {

    public class Program {

        public class Foo {

            public int ID { get; set; }

            public int? Order { get; set; }

​

            public Foo(int id, int? order) {

                ID = id;

                Order = order;

            }

        }

​

        public static void Main(string[] args) {

​

            var ListT = new List<int> {1090,1089};

            var ListTOrder = ListT.Select((x, index) => new { Item = x, Index = index }).ToDictionary(x => x.Item, x => x.Index);

​

            List<Foo> ListB = new List<Foo> {

                new Foo(1089, 1),

                new Foo(1089, 3),

                new Foo(1089, 4),

                new Foo(1089, null),                

                new Foo(1090, 1),

                new Foo(1090, 3),

                new Foo(1090, 4)

            };

​

            ListB = ListB.OrderBy(x => ListTOrder[x.ID]).ThenBy(x => x.Order).ToList();

​

            foreach (var item in ListB) {

                Console.WriteLine(item.ID + " - " + item.Order);

            }

        }

    }

}

​