序列不包含任何元素-IList <T> 有物品

Question

foreach (var i in Model.Items)
{
        string s = "abc" + i.Name;
}

上面的代碼給了我InvalidOperationException，其中消息Sequence不包含任何元素。

Model.Items是IList類型，它包含兩個元素，盡管它在foreach循環中給了我異常。

我在i.Name上應用了watch，它顯示了一個值，但是當執行foreach循環內的行時，它給出了異常。

有什么問題？

堆棧跟蹤

   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
   at ASP._Page_Views_Country_Hotels_cshtml.Execute() in d:\app\myController\items.cshtml:line 15
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy()
   at System.Web.Mvc.WebViewPage.ExecutePageHierarchy()
   at System.Web.WebPages.StartPage.RunPage()
   at System.Web.WebPages.StartPage.ExecutePageHierarchy()
   at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage)
   at System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance)
   at System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer)
   at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context)
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult)
   at System.Web.Mvc.ControllerActionInvoker.<>c__DisplayClass1a.<InvokeActionResultWithFilters>b__17()
   at System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation)

模型類

public class ItemsViewModel 
{
    public Category Category { get; set; }
    public IList<Item> Items { get; set; }
}

第1至15行

@model IPF.Web.Models.ItemsViewModel

@{
    Layout = "_SubLayout.cshtml";
    string desc = "Items of " + Model.Category.Name + ". ";
    string key = "Items of " + Model.Category.Name;
}   

<h1>@string.Format("{0} - Items", Model.Category.Name)</h1>
@if (Model.Items.Count > 0)
{
    IList<Models.Item> items = Model.Items.ToList();//added as suggested
    foreach (var i in items)
    {
        desc += i.Name.ToString() + " ,";//this is where I am getting exception
        //some other stuff
    }
}

物品類別

public class Item
{
     [HiddenInput(DisplayValue = false)]
     public int Id { get; set; }

     [MaxLength(300, ErrorMessage = "Max length can be 300 only.")]
     [Required]
     [Remote("CheckItemName", "Item", AdditionalFields = "Id")]
     public string Name { get; set; }

     [Required]
     [MinLength(50, ErrorMessage = "Min 50 characters should be entered.")]
     [DataType(DataType.MultilineText)]
     [AllowHtml]
     [UIHint("tinymce_jquery_full")]
     public string Description { get; set; }
}

CheckItemName方法

public JsonResult CheckItemName([Bind(Prefix = "Item")]Item oItem)
{
    return Json(!repository.Items.Where(c => c.Id != oItem.Id).Any(c => c.Name == oItem.Name), JsonRequestBehavior.AllowGet);
}

Answer 1

在使用ASP或MVC + SilverLight時，我不建議使用First（）或FirstOrDefault（）。

搜索.First（）; 或.FirstOrDefault（）並添加-> .DefaultIfEmpty（）;