C#语言各个版本特性(二)

二、排序Product

1.按名称对产品进行排序，以特定顺序显示一个列表的最简单方式就是先将列表排序，再遍历并显示其中的项。

C#1.1 使用IComparer对ArrayList进行排序

product类

 using System.Collections;
 using System.ComponentModel;

 namespace Chapter01.CSharp1
 {
     [Description("Listing 1.01")]
     public class Product
     {
         string name;
         public string Name
         {
             get { return name; }
         }

         decimal price;
         public decimal Price
         {
             get { return price; }
         }

         public Product(string name, decimal price)
         {
             this.name = name;
             this.price = price;
         }

         public static ArrayList GetSampleProducts()
         {
             ArrayList list = new ArrayList();
             list.Add(new Product("West Side Story", 9.99m));
             list.Add(new Product("Assassins", 14.99m));
             list.Add(new Product("Frogs", 13.99m));
             list.Add(new Product("Sweeney Todd", 10.99m));
             return list;
         }

         public override string ToString()
         {
             return string.Format("{0}: {1}", name, price);
         }
     }
 }

ArrayListSort类

 using System;
 using System.Collections;
 using System.ComponentModel;

 namespace Chapter01.CSharp1
 {
     [Description("Listing 1.05")]
     class ArrayListSort
     {
         class ProductNameComparer : IComparer
         {
             public int Compare(object x, object y)
             {
                 Product first = (Product)x;
                 Product second = (Product)y;
                 return first.Name.CompareTo(second.Name);
             }
         }

         static void Main()
         {
             ArrayList products = Product.GetSampleProducts();
             products.Sort(new ProductNameComparer());
             foreach (Product product in products)
             {
                 Console.WriteLine(product);
             }
         }
     }
 }

提供一个IComparer实现，比较器。或者Product类实现IComparable。

区别：IComparer和IComparable(比较器接口和可比较的接口)

缺陷：Compare方法中显示强制类型转换，而ArrayList是类型不安全的，转换为对象Product时可能报错。foreach循环中隐式的编译器自动类型转换，转换为Product类型执行时可能报错。

2.C#2.0 引入泛型，使用IComparer<Product>对List<Product>进行排序

product类

 using System.Collections.Generic;
 using System.ComponentModel;

 namespace Chapter01.CSharp2
 {
     [Description("Listing 1.02")]
     public class Product
     {
         string name;
         public string Name
         {
             get { return name; }
             private set { name = value; }
         }

         decimal price;
         public decimal Price
         {
             get { return price; }
             private set { price = value; }
         }

         public Product(string name, decimal price)
         {
             Name = name;
             Price = price;
         }

         public static List<Product> GetSampleProducts()
         {
             List<Product> list = new List<Product>();
             list.Add(new Product("West Side Story", 9.99m));
             list.Add(new Product("Assassins", 14.99m));
             list.Add(new Product("Frogs", 13.99m));
             list.Add(new Product("Sweeney Todd", 10.99m));
             return list;
         }

         public override string ToString()
         {
             return string.Format("{0}: {1}", name, price);
         }
     }
 }

ListSortWithComparer类

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;

 namespace Chapter01.CSharp2
 {
     [Description("Listing 1.06")]
     class ListSortWithComparer
     {
         class ProductNameComparer : IComparer<Product>
         {
             public int Compare(Product first, Product second)
             {
                 return first.Name.CompareTo(second.Name);
             }
         }

         static void Main()
         {
             List<Product> products = Product.GetSampleProducts();
             products.Sort(new ProductNameComparer());
             foreach (Product product in products)
             {
                 Console.WriteLine(product);
             }
         }
     }
 }

使用Comparison<Product>对List<Product>进行排序(C#2)，不需要实现ProductNameComparer比较器类型，只是创建一个委托实例(C#2.0 匿名方法)。

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;

 namespace Chapter01.CSharp2
 {
     [Description("Listing 1.07")]
     class ListSortWithComparisonDelegate
     {
         static void Main()
         {
             List<Product> products = Product.GetSampleProducts();
             products.Sort(delegate(Product first, Product second)
                 { return first.Name.CompareTo(second.Name); }
             );
             foreach (Product product in products)
             {
                 Console.WriteLine(product);
             }
         }
     }
 }

3.C#3.0 Lambda表达式 在Lambda表达式中使用Comparison<Product>进行排序(C#3)

product类

 using System.Collections.Generic;
 using System.ComponentModel;

 namespace Chapter01.CSharp3
 {
     [Description("Listing 1.3")]
     class Product
     {
         public string Name { get; private set; }
         public decimal Price { get; private set; }

         public Product(string name, decimal price)
         {
             Name = name;
             Price = price;
         }

         Product()
         {
         }

         public static List<Product> GetSampleProducts()
         {
             return new List<Product>
             {
                 new Product { Name="West Side Story", Price = 9.99m },
                 new Product { Name="Assassins", Price=14.99m },
                 new Product { Name="Frogs", Price=13.99m },
                 new Product { Name="Sweeney Todd", Price=10.99m}
             };
         }

         public override string ToString()
         {
             return string.Format("{0}: {1}", Name, Price);
         }
     }
 }

ListSortWithLambdaExpression类

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;

 namespace Chapter01.CSharp3
 {
     [Description("Listing 1.08")]
     class ListSortWithLambdaExpression
     {
         static void Main()
         {
             List<Product> products = Product.GetSampleProducts();
             products.Sort(
                 (first, second) => first.Name.CompareTo(second.Name)
             );
             foreach (Product product in products)
             {
                 Console.WriteLine(product);
             }
         }
     }
 }

ListOrderWithExtensionMethod类 使用扩展方法对List<Product>进行排序

 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;

 namespace Chapter01.CSharp3
 {
     [Description("Listing 1.09")]
     class ListOrderWithExtensionMethod
     {
         static void Main()
         {
             List<Product> products = Product.GetSampleProducts();

             foreach (Product product in products.OrderBy(p => p.Name))
             {
                 Console.WriteLine(product);
             }
         }
     }
 }

总结：

→C#1,弱类型的比较功能不支持委托排序。

→C#2,强类型的比较功能，委托比较，匿名方法。

→C#3Lambda表达式，扩展方法,允许列表保持未排序状态。