Question

Can I use a fancy LINQ query to return a List<FileInfo>, by passing it in a method (List<FileInfo> oldList, List<FileInfo> newList), and seeing what differences there are between the two lists?

Basically, I want to get a list of any files added to newList, that were not available in oldList.

Answer 1

Given an IEqualityComparer for FileInfo shown below:

public class FileInfoEqualityComparer : IEqualityComparer<FileInfo>
{
    public bool Equals(FileInfo x, FileInfo y)
    {
        return x.FullName.Equals(y.FullName);
    }

    public int GetHashCode(FileInfo obj)
    {
        return obj.FullName.GetHashCode();
    }
}

You can use following code to find the difference between two lists:

var allItems = newList.Union(oldList);
var commonItems = newList.Intersect(oldList);
var difference = allItems.Except(commonItems, new FileInfoEqualityComparer());

To find items added to newList list, use following code:

var addedItems = newList.Except(oldList, new FileInfoEqualityComparer());