C#开发的进化史

1、数据类型的进化

C#1中实现Product类型代码

 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);
 
         }
 
     }

C#2中的强类型集合和私有的赋值方法

  public class Product
     {
         string name;
         public string Name
         {
             get { return name; }
             private set { Name = value; } 私有的赋值方法
         }
 
         decimal price;
         public decimal Price
         {
             get { return price; }
             private set { Price = value; }
         }
         //C#3:Product(){}
         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);
 
         }
 
     }

C#3自动实现的属性和更简单的初始化

  public class Product
     {
         public string Name { get; private set; }
         public string Price { get; private set; }
 
         public Product(string name, decimal price)
         {
 
               Name = name;
               Price = price;
         }
 
         private 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);
         }
 
     }

C#4中命名实参

 public class Product
     {
 
         public override string ToString()
         {
             return string.Format("{0}: {1}", name, price);
         }
         //C#4中的参数：尽管私有赋值不能被公共的改变，但如果要求它也不能被私有的改变，将会更加的清晰，在C#4中，我们用调用构造函数时指定实参的名称
         readonly string name;
         public string Name { get { return name; } }
         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},
         };
 
     }

2、排序和过滤的演化

1、排序

C#1中使用IComparer对ArrayList进行排序

 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);
             }
         }

C#2中使用IComparer<product>对List<Product>进行排序

  class ProductNameComparer : IComparer<Product>
         {
             public int Compare(Product x, Product y)
             {
                 return x.Name.CompareTo(y.Name);
             }
         }
 static void Main()
 {
  List<Product> products = Product.GetSampleProducts();
  products.Sort(new ProductNameComparer());
             foreach (Product product in products)
             {
                 Console.WriteLine(product);
             }
 }

C#2中使用委托进行比较

  /*
          * C#2的方法1确实有了一定的改进，但是我们希望能直接指定要进行的标胶，就能开始对产品进行排序，而不需要实现一个接口来做这件事
          * 下面它告诉sort方法如何用一个委托来比较俩个产品.省略了接口实现的代码和products.Sort(new ProductNameComparer());
          * List<Product> products = Product.GetSampleProducts();
          * products.Sort（delegate （Product x，Product y）
          * {return x.Name.CompareTo(y.Name);}
          * ）;
          */

C#3中使用lambda表达式进行比较

  List<Product> products = Product.GetSampleProducts();
 products.Sort(（x,y）=>x.Name.CompareTo(y.Name));
 foreach（Product product in products）
 {
          console.writeline(product);
 }
 C#3还有另一种写法排序
 foreach（Product product in product.OrderBy（p=>p.Name））
 {
          console.writeline(product);//通知轻松的按顺序打印名称，同时不必修改原产品列表
 }

2、查询

循环、测试和打印（C#1）

  ArrayList products = Product.GetSampleProducts();
             foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
             {
                 Console.WriteLine(product);
             }

测试和打印分开进行（C#2）

 List<Product> products =Product.GetSampleProducts();
           Predicate<Product> test = delegate(Product p){ return p.Price > 10m;};
            List<Product>  matches=products.FindAll(test);
           Action<Product> print=console.writeLine;
           matches.ForEach(print);

测试和打印分开进行的另一个版本（C#2）

List<Product> products =Product.GetSampleProducts();
products.FindAll（delegate （Product p）{ return p.Price >;}）.ForEach(Console.WriteLine);

用lambda表达式来进行测试（c#3）

List<Product> products =Product.GetSampleProducts();
foreach（Product product in products.Where（p=>p.price>））
{
    Console.WriteLine(product);
}
              

C#中使用Linq表达式

foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
{
Console.WriteLine(product);
}