Csharp 2000 things - Item 135: #135 – Implementing IComparable to Allow Sorting a Custom Type

CSharp2000things_Item135.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ArraySort_Example
{
    /// <summary>
    /// Oct. 25, 2017
    /// Julia learns C# 2000 things 
    /// #135 – Implementing IComparable to Allow Sorting a Custom Type
    /// https://csharp.2000things.com/2010/10/30/135-implementing-icomparable-to-allow-sorting-a-custom-type/
    /// Arrays of elements that belong to a custom type cannot be sorted, unless the type implements 
    /// the IComparable interface.
    /// 
    /// To make elements of a custom type sortable, you need to implement IComparable in your type.  
    /// IComparable consists of the single method CompareTo, which compares two objects.
    /// 
    /// Here’s an example of a Person class implementing CompareTo to sort people in LastName/FirstName order:
    /// </summary>
    class Person : IComparable
    {
        public string FirstName { get; set; }
        public string LastName  { get; set; }

        public Person(string firstName, string lastName)
        {
            FirstName = firstName;
            LastName  = lastName; 
        }

        /// <summary>
        /// CompareTo 
        /// </summary>
        /// <param name="obj"></param>
        /// <returns></returns>
        public int CompareTo(object obj)
        {
            Person other = obj as Person;

            if (other == null)
            {
                throw new ArgumentException("Object is not a Person");
            }
            else
            {
                // Sort by LastName, then by FirstName (ignore case)
                int compare = this.LastName.ToLower().CompareTo(other.LastName.ToLower());
                if (compare == 0)
                {
                    compare = this.FirstName.ToLower().CompareTo(other.FirstName.ToLower());
                }

                return compare;
            }
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Person[] folks = new Person[4];
            folks[0] = new Person("Bronte", "Emily");
            folks[1] = new Person("Bronte", "Charlotte");
            folks[2] = new Person("Tennyson", "Alfred");
            folks[3] = new Person("Mailer", "Norman");
            Array.Sort(folks);    // C. Bronte, E. Bronte, Mailer, Tennyson
        }        
    }
}