如何将项添加到IEnumerable SelectListItem

Question

我正在尝试将项添加到IEnumerable SelectList.我有一个初始查询填充我的列表,然后我有一个查询来检查是否存在名为"INFORMATIONAL"的项目.如果没有,我需要将它添加到从我的初始查询返回的列表中.这是我的代码.它不喜欢list.Add(newItem).任何援助将不胜感激.谢谢

public IEnumerable<SelectListItem> GetCategoriesByAccountID(string AccountID)
    {
        IEnumerable<SelectListItem> list = null;

        using (var context = new AMPEntities())
        {
            // Queries DB for list of categories by AccountID
            var query = (from ca in context.CustomAlerts
                        where ca.AccountID == AccountID
                        orderby ca.AlertCategory
                        select new SelectListItem { Text = ca.AlertCategory, Value = ca.AlertCategory }).Distinct();
            list = query.ToList();

            // Checks list to see if "INFORMATIONAL" already exists
            var item = (from l in list
                        where l.Value == "INFORMATIONAL"
                        select new SelectListItem { Text = l.Text, Value = l.Value }).FirstOrDefault();

            // If "INFORMATIONAL" is not present add it to list
            if (item == null)
            {
                var newItem = new SelectListItem { Text = "INFORMATIONAL", Value = "INFORMATIONAL" };
                list.Add(newItem);
            }
        }

        return list;
    }

Answer 1

问题是你的变量是类型的IEnumerable<SelectListItem>.将其更改为List<SelectListItem>或使用其他变量.

public IEnumerable<SelectListItem> GetCategoriesByAccountID(string AccountID)
    {
        List<SelectListItem> list = null;

        using (var context = new AMPEntities())
        {
            // Queries DB for list of categories by AccountID
            var query = (from ca in context.CustomAlerts
                        where ca.AccountID == AccountID
                        orderby ca.AlertCategory
                        select new SelectListItem { Text = ca.AlertCategory, Value = ca.AlertCategory }).Distinct();
            list = query.ToList();

            // Checks list to see if "INFORMATIONAL" already exists
            var item = (from l in list
                        where l.Value == "INFORMATIONAL"
                        select new SelectListItem { Text = l.Text, Value = l.Value }).FirstOrDefault();

            // If "INFORMATIONAL" is not present add it to list
            if (item == null)
            {
                var newItem = new SelectListItem { Text = "INFORMATIONAL", Value = "INFORMATIONAL" };
                list.Add(newItem);
            }
        }

        return list;
    }