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)));     } }