Compareto Method

The compareTo method is used for sorting collection of class instances.

The method is also an implementation of the Comparable interface. It can be applied to lists.

Syntax

Interface implementation:

CompareTo method:

Sorting class collection via the compareTo method:

Examples

Ascending Sort

using System;
using System.Collections.Generic;

namespace ConsoleApp1
{
    class Smartphone : IComparable
    {
        public string model { get; set; }
        public double price { get; set; }

public Smartphone(string model, double price)
        {
            this.model = model;
            this.price = price;
        }

public int CompareTo(object obj)
        {
            Smartphone smartphone = (Smartphone)obj;

if (smartphone.price > this.price)
            {
                return -1;
            }
            else if (smartphone.price == this.price)
            {
                return 0;
            }

return 1;
        }
    }

class Shop
    {
        public List<Smartphone> smartphones;

public Shop()
        {
            this.smartphones = new List<Smartphone>();
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            Shop shop = new Shop();

Smartphone phone_1 = new Smartphone("Samsung Galaxy S 20", 1300);
            Smartphone phone_2 = new Smartphone("Iphone 11", 2600);
            Smartphone phone_3 = new Smartphone("Samsung Galaxy Fold", 2400);

shop.smartphones.Add(phone_1);
            shop.smartphones.Add(phone_2);
            shop.smartphones.Add(phone_3);

// Sorting collection via the compareTo method:
            shop.smartphones.Sort();

foreach (Smartphone smartphone in shop.smartphones)
            {
                Console.WriteLine("--------");
                Console.WriteLine(smartphone.model);
                Console.WriteLine(smartphone.price);
            }
        }
    }
}

Output:

Explanation:

At lines 17 - 31 the CompareTo method is defined. It's used to sort the phones by price ascending.
If at line 21 the sign > is changed to <, the phones will be sorted by descending.
At line 60 the collection of phones is sorted. The sorting uses the CompareTo method.

Descending Sort