對象引用不設置到對象的實例

Question

請看看這個圖片：通過「TopTens」 IM我看來

我要循環，我們可以看到，有9個對象在 「TopTens」，爲什麼dooes它說：對象引用未設置爲對象的實例？

！[在這裏輸入的形象描述] [1]

[NullReferenceException: Object reference not set to an instance of an object.] 
    ASP._Page_Views_secure_CreatePageDetailss_cshtml.Execute() in c:\Users\xxx\xxx\xxxx\xxxxx\xxxxx\Views\Secure\CreatePageDetailss.cshtml:18 
    System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +271 
    System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +120 
    System.Web.WebPages.StartPage.RunPage() +63 
    System.Web.WebPages.StartPage.ExecutePageHierarchy() +100 
    System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +131 
    System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +695 
    System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +382 
    System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +431 
    System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +39 
    System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +116 
    System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +529 
    System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +106 
    System.Web.Mvc.Async.<>c__DisplayClass2b.<BeginInvokeAction>b__1c() +321 
    System.Web.Mvc.Async.<>c__DisplayClass21.<BeginInvokeAction>b__1e(IAsyncResult asyncResult) +185 
    System.Web.Mvc.Async.WrappedAsyncResult`1.CallEndDelegate(IAsyncResult asyncResult) +42 
    System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +133 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +56 
    System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +40 
    System.Web.Mvc.Controller.<BeginExecuteCore>b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) +34 
    System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +70 
    System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +139 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +59 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 
    System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +44 
    System.Web.Mvc.Controller.<BeginExecute>b__15(IAsyncResult asyncResult, Controller controller) +39 
    System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +62 
    System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +139 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +59 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 
    System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +39 
    System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.EndExecute(IAsyncResult asyncResult) +39 
    System.Web.Mvc.MvcHandler.<BeginProcessRequest>b__5(IAsyncResult asyncResult, ProcessRequestState innerState) +39 
    System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +70 
    System.Web.Mvc.Async.WrappedAsyncResultBase`1.End() +139 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +59 
    System.Web.Mvc.Async.AsyncResultWrapper.End(IAsyncResult asyncResult, Object tag) +40 
    System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +40 
    System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +38 
    System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +9514928 
    System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +155 

Answer 1

只有一個你給我們的代碼解釋，那就是在你的列表中的一個產品null。

然後@item.LongDesc將發出NullReferenceException。

如果允許在TopTens的項目之一是null，添加一個檢查NULL：

@if (@item != null) 
{ 
    <p>@item.LongDesc</p> 
} 

或者，如果TopTens是List只是不添加更多的項目則有，防一個是null。