C# Beginner: Where has my IList.Where() method gone?

I've got another simple one (I think) that's stumping me. I have written a method in one of my controls that gets the latest version of a file in a CMS given it's filename (i.e. regardless of what folder the file resides in). I found it useful enough that I thought I'd chuck it in my CMSToolbox class, but when I do this I can no longer use the Where() method of a FileManager class provided by the CMS (which returns a list).

Here's a simplified example of my class:

using System;
using System.Collections.Generic;
using CMS.CMS;
using CMS.Core;
using CMS.Web;

namespace CoA.CMS {
    public class ToolBox
    {
        public CMS.CMS.File getLatestFileVersionByFilename(string filename, int GroupID)
        {
            IList<CMS.CMS.File> fileWithName = FileManager.GetGroupAll(false, GroupID).Where(file => currentFileVersionIsNamed(file, filename)).ToList<CMS.CMS.File>();
            return getLatestFileFromListOfFiles(fileWithName);

        }
        protected bool currentFileVersionIsNamed(CMS.CMS.File file, string name)
        {
        }
        protected CMS.CMS.File  getLatestFileFromListOfFiles(CMS.CMS.File file)
        {
        }
    }
}

When I do exactly the same thing in the context of a Control (really a class provided by the CMS which extends Control) I have access to the Where() method, but in my ToolBox class 开发者_StackOverflowI don't. What gives? I figured that an IList would always allow access to the same methods from wherever you use it.

I'm a wrong again, haha :)

Edit: Filemanager.GetGroupAll() returns a CMSList which extends IList

You need a using directive for System.Linq. .Where() is an extension method on IEnumerable<T> (which IList<T> implements) that is defined in the System.Linq namespace.

Joel was first, but to expand on that: Where() is an extension method. Extension methods are static methods that act like real methods, and are declared like this:

static class NameNeverUsed
{
    public static void AnExtensionMethod(this string x)
    {
    }
}

And called like:

"hello".AnExtensionMethod();

They need to imported by using statements like anything else. So unlike Java/C++ a class can have methods declared outside it.

IIRC, that .Where method is part of LINQ, and you need to add those using statements in your class to get the extension methods for the IEumerable interface.