.NET IComparer排序错误

Question

I have run into a very weird issue recently. I deployed a new version of a program and am receiving this error when the IComparer.Compare() method gets called internally:

Unable to sort because the IComparer.Compare0 method returns inconsistent
results. Either a value does not compare equal to itself, or one value     repeatedly
compared to another value yields different results. x:",x's type: 'String',
IComparer.".

The odd thing is that I cannot reproduce this issue on my computer. It doesn't happen for me in Visual Studio 2013 (debug or release versions) and it doesn't happen when I install the application either. To make things weirder, it doesn't even happen on every computer in production, only about 30% of them.

My application targets .NET Framework 4 and the platform target is x86.

There is only one instance of an IComparer object in my code, here it is:

public int Compare(string stringOne, string stringTwo)
{
    if (stringOne == stringTwo) { return 0; }
    else if (stringOne == null) { return stringTwo == null ? 0 : -1; }
    else if (stringTwo == null) { return stringOne == null ? 0 : 1; }

    else if (stringOne.StartsWith("_") && !stringTwo.StartsWith("_"))
    {
        return -1;
    }
    else if (!stringOne.StartsWith("_") && stringTwo.StartsWith("_"))
    {
        return 1;
    }
    else if ((stringOne.StartsWith("l") || stringOne.StartsWith("L")) &&
            (!stringTwo.StartsWith("l") || !stringTwo.StartsWith("L")))
    {
        return -1;
    }
    else if ((!stringOne.StartsWith("l") || !stringOne.StartsWith("L")) &&
              (stringTwo.StartsWith("l") || stringTwo.StartsWith("L")))
    {
        return 1;
    }
    else
    {
        if (stringTwo == null) { return 1; }
        else { return stringOne.CompareTo(stringTwo) == 1 ? -1 : 1; }
    }
}

Has anyone else had this issue and found a solution to it? Does my comparer look it covers all cases? I am totally lost about this issue and have no idea what to try next. Any help will be greatly appreciated.

Answer 1

This

else if ((stringOne.StartsWith("l") || stringOne.StartsWith("L")) &&
            (!stringTwo.StartsWith("l") || !stringTwo.StartsWith("L")))
    {
        return -1;
    }
    else if ((!stringOne.StartsWith("l") || !stringOne.StartsWith("L")) &&
              (stringTwo.StartsWith("l") || stringTwo.StartsWith("L")))
    {
        return 1;
    }

should be

else if ((stringOne.StartsWith("l") || stringOne.StartsWith("L")) &&
            !(stringTwo.StartsWith("l") || stringTwo.StartsWith("L")))
    {
        return -1;
    }
    else if (!(stringOne.StartsWith("l") || stringOne.StartsWith("L")) &&
              (stringTwo.StartsWith("l") || stringTwo.StartsWith("L")))
    {
        return 1;
    }

As a side note, the way you wrote this comparer function is highly ineffecient.