c# - 无法将类型 Void 隐式转换为类型 System.Collections.Generic.IList<T>

Question

尝试返回泛型类型时出现标题中描述的错误。 我确定我在做一些愚蠢的事情 - 建议感谢...

public static IList<T> GetGroupById<T>(int groupId)
        {

            DashboardGroupType type = (DashboardGroupType)groupId;
            IList<T> result = null;

            var obj = default(T);

            switch (type)
            {
                case DashboardGroupType.Countries:
                    break;
                case DashboardGroupType.Customers:
                    // this returns a list of typ  IEnumerable<Customer>
                    obj = (T) CustomerRepository.GetAllCustomers();
                    break;
                case DashboardGroupType.Facilities:
                    // this returns a list of typ  IEnumerable<Facility>
                    obj = (T) FacilityRepository.GetAllFacilities();
                    break;
                case DashboardGroupType.Heiarchy:
                    break;
                case DashboardGroupType.Lines:
                    break;
                case DashboardGroupType.Regions:
                    // this returns a list of typ  IEnumerable<string>
                    obj = (T) CustomerRepository.GetRegionsHavingCustomers();
                    break;
                case DashboardGroupType.States:
                    // // this returns a list of typ  IEnumerable<Customer>
                    obj = (T) CustomerRepository.GetStatesHavingCustomers();
                    break;
                case DashboardGroupType.Tanks:
                    break;
                default:
                    break;
            }

            result = result.Add(obj); // ERROR IS THROWN HERE

        }

Answer 1

result = result.Add(obj);

Add() 不返回任何东西。 删除“结果=”