How do I use the IComparable interface?

Question

I need a basic example of how to use the IComparable interface so that I can sort in ascending or descending order and by different fields of the object type I'm sorting.

Answer 1

Well, since you are using List<T> it would be a lot simpler to just use a Comparison<T>, for example:

List<Foo> data = ...
// sort by name descending
data.Sort((x,y) => -x.Name.CompareTo(y.Name));

Of course, with LINQ you could just use:

var ordered = data.OrderByDescending(x=>x.Name);

But you can re-introduce this in List<T> (for in-place re-ordering) quite easily; Here's an example that allows Sort on List<T> with lambda syntax:

using System;
using System.Collections.Generic;  

class Foo { // formatted for vertical space
    public string Bar{get;set;}
}
static class Program {
    static void Main() {
        List<Foo> data = new List<Foo> {
            new Foo {Bar = "abc"}, new Foo {Bar = "jkl"},
            new Foo {Bar = "def"}, new Foo {Bar = "ghi"}
        };
        data.SortDescending(x => x.Bar);
        foreach (var row in data) {
            Console.WriteLine(row.Bar);
        }
    }

    static void Sort<TSource, TValue>(this List<TSource> source,
            Func<TSource, TValue> selector) {
        var comparer = Comparer<TValue>.Default;
        source.Sort((x,y)=>comparer.Compare(selector(x),selector(y)));
    }
    static void SortDescending<TSource, TValue>(this List<TSource> source,
            Func<TSource, TValue> selector) {
        var comparer = Comparer<TValue>.Default;
        source.Sort((x,y)=>comparer.Compare(selector(y),selector(x)));
    }
}