C#教程之C#语言各个版本特性

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C#教程之C#语言各个版本特性

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。

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