C# - IComparer - If datetime is null then should be sorted to the bottom not the top

Question

I have a list of dates that I want to sort in an ascending order. However, the default comparer means that I have:

null
null
18/01/2011
23/01/2011

Answer 1

Here's a generic comparer that should work for pretty much any type:

var yourList = new List
                   {
                       null, new DateTime(2011, 1, 23),
                       null, new DateTime(2011, 1, 18)
                   };

var comparer = new NullsLastComparer();
yourList.Sort(comparer);  // now contains { 18/01/2011, 23/01/2011, null, null }

// ...

public sealed class NullsLastComparer : Comparer
{
    private readonly IComparer _comparer;

    public NullsLastComparer() : this(null) { }

    public NullsLastComparer(IComparer comparer)
    {
        _comparer = comparer ?? Comparer.Default;
    }

    public override int Compare(T x, T y)
    {
        if (x == null)
            return (y == null) ? 0 : 1;

        if (y == null)
            return -1;

        return _comparer.Compare(x, y);
    }
}