为什么我只能在此IEnumerable <>中获得null

Question

I'm trying to populate this IEnumerable with values from a db.

I can't see what I'm doing wrong.

IEnumerable<Categories> categories = new List<Categories>();

List<SelectListItem> catItems = new List<SelectListItem>();

foreach (var cats in categories)
{
    catItems.Add(new SelectListItem
                     {
                         Text = cats.CategoryName,
                         Value = cats.CategoryID.ToString()
                     });
}

Here is the class:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel.DataAnnotations;
using System.Web.Mvc;

namespace SportsStore.Domain.Entities
{
    public class Categories
    {
        [Key]
        public int CategoryID { get; set; }
        public string CategoryName { get; set; }
    }

}

Answer 1

您只需初始化一个新的类别集合，就不会添加任何类别。

Answer 2

How are you populating the categories list? It won't just get filled by saying...

IEnumerable<Categories> categories = new List<Categories>(); 

You need populate it somehow.

Answer 3

Because here you create a new (and empty) list of Categories:

IEnumerable<Categories> categories = new List<Categories>();

and here you try to iterate over the empty list:

foreach (var cats in categories)
{

Which means you're never adding anything to cat.Items