[C#] IComparable 和 IComparer

這篇文章 如何使用 IComparable 和 IComparer 介面視覺 C# 內容，剛好跟遠距教學內容差依不大，拿它來進行排序練習

建立兩個 Project，分別為 ClassDemo Project 和 Show Project

ClassDemo Project

using System.Collections.Generic;
using System.Collections; // IComparer interface 在 System.Collections namespace 內

namespace ClassDemo
{
    public class Car
    {
        public string Maker { get; set; }
        public int Year { get; set; }
        public decimal Price { get; set; }
  
        class SortByMaker : IComparer
        {
            public int Compare(object x, object y)
            {
                Car x1 = x as Car;
                Car y1 = y as Car;
                return x1.Maker.CompareTo(y1.Maker);
            }
        }

        class SortByMakerDesc : IComparer
        {
           public int Compare(object x, object y)
           {
               Car x1 = x as Car;
               Car y1 = y as Car;
               return y1.Maker.CompareTo(x1.Maker);
           }
        }

        class SortByYear : IComparer
        {
            public int Compare(object x, object y)
            {
                Car x1 = x as Car;
                Car y1 = y as Car;
                return x1.Year.CompareTo(y1.Year);
            }
        }

        class SortByYearDesc : IComparer
        {
            public int Compare(object x, object y)
            {
                Car x1 = x as Car;
                Car y1 = y as Car;
                return y1.Year.CompareTo(x1.Year);
            }
        }

        class SortByPrice : IComparer
        {
            public int Compare(object x, object y)
            {
                Car x1 = x as Car;
                Car y1 = y as Car;
                return x1.Price.CompareTo(y1.Price);
            }
        }

        class SortByPriceDesc : IComparer
        {
            public int Compare(object x, object y)
            {
                Car x1 = x as Car;
                Car y1 = y as Car;
                return y1.Price.CompareTo(x1.Price);
            }
        }

        private static IComparer[] Sorters = new IComparer[]
        {
            new SortByMaker(),
            new SortByMakerDesc(),
            new SortByYear(),
            new SortByYearDesc(),
            new SortByPrice(),
            new SortByPriceDesc(),
        };
  
        public static IComparer 依廠牌排序
        {
            get { return Sorters[0];}
        }

        public static IComparer 依廠牌遞減排序
        {
            get { return Sorters[1]; }
        }

        public static IComparer 依年份排序
        {
            get { return Sorters[2]; }
        }

        public static IComparer 依年份遞減排序
        {
            get { return Sorters[3]; }
        }

        public static IComparer 依價格排序
        {
            get { return Sorters[4]; }
        }

        public static IComparer 依價格遞減排序
        {
            get { return Sorters[5]; }
        }

        public override string ToString()
        {
            return string.Format("{0} - {1} - {2}", this.Maker, this.Year, this.Price);
        }
    }
}

Show Project

using ClassDemo;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

        Car[] arr = new Car[]
        {
            new Car(){Maker = "Ford", Year = 1992, Price = 2500},
            new Car(){Maker = "Fiat",Year = 1988,Price = 1500},
            new Car(){Maker = "Buick",Year = 1932,Price = 2400},
            new Car(){Maker = "Ford", Year = 1932, Price = 1300},
            new Car(){Maker = "Dodge",Year = 1999,Price = 1000},
            new Car(){Maker = "Honda",Year = 1977,Price = 5600}
        };

        Array.Sort(arr,Car.依年份排序);
        foreach (Car item in arr)
        {
            Response.Write(item.ToString() + "＜br/＞");
        }
    }
}

從下圖中可以看見可以選擇要的排序條件

顯示結果

參考資料
• 自訂類別實作 IComparable 介面以執行排序
• [Design Pattern]Decorator Pattern with IComparer － 先比這個，再比那個
  
• [C#]自訂的 Class 繼承自 IComparable 以便具有 Sorting 功能
  
• [轉載] C# 比較和排序（IComparable和IComparer以及它們的泛型實現）