如果Any（）为true，为什么LINQ在Count（）上抛出空引用错误？

Question

I have a question - why do I get a null reference exception at the .Count() method of this IEnumerable if the .Any() returns true?

 Logger.Normal("{0}", targetWorkflow.GetStages().Any() ? "any is true!" : "any is false");
 Logger.Normal("{0}", targetWorkflow.GetStages().Count());

Error:

StackTrace = [ at Sth.Workflow.<GetStages>d__13.MoveNext()XX at System.Linq.Enumerable.Count[TSource]

To be honest, I would expect that the Count() method should return at least 1 if .Any() is true, while if Any() was false, it would return 0?

Let me know where I am wrong, please.

Also - please note that I am not trying to fix the actual problem, I am trying to understand why Any() == true does not ensure that the collection is healthy and 'countable'.

Answer 1

GetStages() appears to be throwing an exception internally within its own code when generating some item that isn't the first item in the sequence. Any can stop as soon as it gets the first item, which is why it's not throwing any exception, but Count needs to iterate the entire sequence in order to get its result.

There is some bug internally in the GetStages() method (or some violation of it's intended usage that you're making) that is unrelated to the code that you've shown.