为什么list.Contains（x）在list包含x，y，z时找不到x

Question

ACCEPTED THE FIRST COMPLETE ANSWER GIVEN.

THANKS TO ALL WHO RESPONDED!

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I'm new to C# and Visual Studio so forgive me if this is an elementary question.

if (!exceptions.Contains(accountNodeID))
{
     dummyTotals.Add(accountNodeID, accountNodeTotal);
}

• exceptions is a List<string>
• accountNodeID is a string
• dummyTotals is a Dictionary<string, int>

If exceptions consists of only one element, Contains DOES recognize when accountNodeID is in exceptions .

If exceptions consists of 2+ elements, Contains DOES NOT recognize when accountNodeID is in exceptions .

Screenshots of Visual Studio debugger [which SO won't allow me to post here because I had to create a new account :( ]:

• accountNodeID is in exceptions , but is added to dummyTotals anyway .
• but that doesn't happen when exceptions contains only one element .

Can anyone tell me the following?

1. Why Contains doesn't recognize that accountNodeID is one among several elements in exceptions -- my code certainly looks like all of the examples I can find, so far as I can tell
2. How to prevent accountNodeID from being added to dummyTotals when it is among several elements in exceptions

Very happy to provide additional relevant info, as needed! Thanks very much!!!

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EDIT

Thank you for the info that has been supplied already. I'm looking over it now. For the record, the following is how the list is being created (iterating over nodes in an XML file and using Add ).

        List<string> dummyList = new List<string>();

        while (exceptionsIterator.MoveNext())
        {
            exceptions.Add(exceptionsIterator.Current.Value); 

        }

I thought this was adding list elements rather than concatenating values onto a string.

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EDIT

See my final comment on the answer for the ultimate resolution to this problem.

Answer 1

Your debugging screenshot shows that exceptions only contains one element: "541 139 434"

So the fault must lie in how exceptions is populated.

When you add to a List<string> , you do so by calling .Add(string) . I suspect there is code like:

List<string> exceptions = new List<string>(String.Join(" ", accountNodeIds));

This is NOT the way to populate a list. Instead:

List<string> exceptions = new List<string>(accountNodeIds);

or

exceptions.AddRange(accountNodeIds);

or

foreach (string accountNodeId in accountNodeIds) {
    exceptions.Add(accountNodeId);
}

Answer 2

List.Contains just loooks if the object inside equals another object, in case of string it looks if the whole string matches. You are looking for a substring since "541 139 434" is not the same as "139".

You can use String.Contains with Enumerable.Any :

if (!exceptions.Any(e => e.Contains(accountNodeID)))
{
     dummyTotals.Add(accountNodeID, accountNodeTotal);
}

You could also check if one of the "words" in the string (separated by white-space) is the one you're looking for, therefore use String.Split :

if (!exceptions.Any(e => e.Split().Contains(accountNodeID)))
{
}

Answer 3

Because it looks for the exact match.Instead you should use Any , in order to check whether any of your elements Contains your accountNodeId :

if (!exceptions.Any(x => x.Contains(accountNodeID))

Or don't do this.Store your Ids seperately into your List .Each item should contain one Id .Then you can use Contains and you will get the expected result.