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

 1 public class Product
 2     {
 3         string name;
 4         public string Name
 5         {
 6             get { return name; }
 7         }
 8 
 9         decimal price;
10         public decimal Price
11         {
12             get { return price; }
13         }
14 
15         public Product(string name, decimal price)
16         {
17             this.name = name;
18             this.price = price;
19         }
20      
21         public static ArrayList GetSampleProducts()
22         {
23             ArrayList list = new ArrayList();
24             list.Add(new Product("West Side Story", 9.99m));
25             list.Add(new Product("Assassins", 14.99m));
26             list.Add(new Product("Frogs", 13.99m));
27             list.Add(new Product("Sweeney Todd", 10.99m));
28             return list;
29            
30         }
31 
32         public override string ToString()
33         {
34             return string.Format("{0}: {1}", name, price);
35           
36         }
37       
38 
39     }

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C#2中的强类型集合和私有的赋值方法

 1  public class Product
 2     {
 3         string name;
 4         public string Name
 5         {
 6             get { return name; }
 7             private set { Name = value; } 私有的赋值方法
 8         }
 9 
10         decimal price;
11         public decimal Price
12         {
13             get { return price; }
14             private set { Price = value; }
15         }
16         //C#3:Product(){}
17         public Product(string name, decimal price)
18         {
19            
20               Name = name;
21               Price = price;
22         }
23       public static List<Product>GetSampleProducts()
24         {
25              List<Product>list= new List<Product>();
26             list.Add(new Product("West Side Story", 9.99m));
27             list.Add(new Product("Assassins", 14.99m));
28             list.Add(new Product("Frogs", 13.99m));
29             list.Add(new Product("Sweeney Todd", 10.99m));
30             return list;
31            
32         }
33 
34         public override string ToString()
35         {
36             return string.Format("{0}: {1}", name, price);
37           
38         }
39 
40     }

View Code

C#3自动实现的属性和更简单的初始化

 1  public class Product
 2     {
 3         public string Name { get; private set; }
 4         public string Price { get; private set; }
 5 
 6         public Product(string name, decimal price)
 7         {
 8            
 9               Name = name;
10               Price = price;
11         }
12 
13         private Product()
14         {
15         }
16 
17         public static List<Product> GetSampleProducts()
18         {
19             return new List<Product>
20             {
21                 new Product {Name = "West Side Story", Price = 9.99m},
22                 new Product {Name = "Assassins", Price = 14.99m},
23                 new Product {Name = "Frogs", Price = 13.99m},
24                 new Product {Name = "Sweeney Todd", Price = 10.99m}
25             };
26         }
27 
28         public override string ToString()
29         {
30             return string.Format("{0}: {1}", Name, Price);
31         }
32       
33     }

View Code

C#4中命名实参

 1 public class Product
 2     {
 3      
 4         public override string ToString()
 5         {
 6             return string.Format("{0}: {1}", name, price);
 7         }
 8         //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
 9         readonly string name;
10         public string Name { get { return name; } }
11         return new List<Product>
12         {
13             new Product {name = "West Side Story", price = 9.99m},
14             new Product {name = "Assassins", price = 14.99m},
15             new Product {name = "Frogs", price = 13.99m},
16             new Product {name = "Sweeney Todd", price = 10.99m},
17         };
18 
19 
20     }

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2、排序和过滤的演化

1、排序

C#1中使用IComparer对ArrayList进行排序

 1 class ProductNameComparer : IComparer
 2         {
 3             public int Compare(object x, object y)
 4             {
 5                 Product first = (Product)x;
 6                 Product second = (Product)y;
 7                 return first.Name.CompareTo(second.Name);
 8             }
 9         }
10  static void Main()
11         {
12             ArrayList products = Product.GetSampleProducts();
13             products.Sort(new ProductNameComparer());
14             foreach (Product product in products)
15             {
16                 Console.WriteLine(product);
17             }
18         }

View Code

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

 1  class ProductNameComparer : IComparer<Product>
 2         {
 3             public int Compare(Product x, Product y)
 4             {
 5                 return x.Name.CompareTo(y.Name);
 6             }
 7         }
 8 static void Main()
 9 {
10  List<Product> products = Product.GetSampleProducts();
11  products.Sort(new ProductNameComparer());
12             foreach (Product product in products)
13             {
14                 Console.WriteLine(product);
15             }
16 }

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C#2中使用委托进行比较

1  /* 
2          * 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
3          * 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());
4          * List<Product> products = Product.GetSampleProducts();
5          * products.Sort（delegate （Product x，Product y）
6          * {return x.Name.CompareTo(y.Name);}
7          * ）;
8          */

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C#3中使用lambda表达式进行比较

 1  List<Product> products = Product.GetSampleProducts();
 2 products.Sort(（x,y）=>x.Name.CompareTo(y.Name));
 3 foreach（Product product in products）
 4 {
 5          console.writeline(product);
 6 }
 7 C#3还有另一种写法排序
 8 foreach（Product product in product.OrderBy（p=>p.Name））
 9 {
10          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
11 }

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2、查询

循环、测试和打印（C#1）

1  ArrayList products = Product.GetSampleProducts();
2             foreach (Product product in products.Cast<Product>().Where(product => product.Price > 10m))
3             {
4                 Console.WriteLine(product);
5             }

View Code

测试和打印分开进行（C#2）

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

View Code

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 >10;}）.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>10））
{
    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);
}