linq排序中的System.NullReferenceException排序OrderBy(a => a.Url),UWP

Question

我有一个ObservableCollection,我甚至先检查它以确保它有元素.然而,我仍然得到一个nullReferenceException(有时候,这从未出现过winrt 8.1版本的问题,我将其更改为UWP.)代码如下,它给出了错误,其中a.Url是:

if (sTumblrblog_gv_list.Count != 0)
{
    if (tumblogconfig.ShowNSFWBlogs)
        sTumblrGridView.ItemsSource = sTumblrblog_gv_list.OrderBy(a => a.Url);
    else
        sTumblrGridView.ItemsSource = sTumblrblog_gv_list.OrderBy(a => a.Url).Where(a => a.IsNsfw == false);
}

System.NullReferenceException was unhandled by user code
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=Tumblr-FIA
  StackTrace:
       at tumblr_fia.MainPage.<>c.<updatestats>b__47_1(sTumblrblog_gv a)
       at System.Linq.EnumerableSorter`2.ComputeKeys(TElement[] elements, Int32 count)
       at System.Linq.EnumerableSorter`1.Sort(TElement[] elements, Int32 count)
       at System.Linq.OrderedEnumerable`1.<GetEnumerator>d__1.MoveNext()
       at System.Runtime.InteropServices.WindowsRuntime.EnumeratorToIteratorAdapter`1.MoveN

ext()
       at System.Runtime.InteropServices.WindowsRuntime.EnumeratorToIteratorAdapter`1.get_HasCurrent()
  InnerException: 

我理解这个错误我相信,但我检查sTumblrblog_gv_list不是空值.而我现在有一个尝试和捕获.有时我还会收到错误.

Answer 1

你可以试试

.OrderBy(a => a != null ? a.Url : null)

在C#6上你有语法

.OrderBy(a => a?.Url)