举例讲解C#中自动实现的属性

当你声明一个 private set 取值函数时，你无法使用对象初始值设定项来初始化属性。 你必须使用构造函数或工厂方法。
示例
下面的示例演示了实现具有自动实现属性的不可变类的两种方法。 这两种方法均使用 private set 声明其中一个属性，使用单独的 get 声明另一个属性。 第一个类仅使用构造函数来初始化属性，第二个类则使用可调用构造函数的静态工厂方法。

// This class is immutable. After an object is created, 
  // it cannot be modified from outside the class. It uses a 
  // constructor to initialize its properties. 
  class Contact
  {
    // Read-only properties. 
    public string Name { get; }
    public string Address { get; private set; }

    // Public constructor. 
    public Contact(string contactName, string contactAddress)
    {
      Name = contactName;
      Address = contactAddress;        
    }
  }

  // This class is immutable. After an object is created, 
  // it cannot be modified from outside the class. It uses a 
  // static method and private constructor to initialize its properties.  
  public class Contact2
  {
    // Read-only properties. 
    public string Name { get; private set; }
    public string Address { get; }

    // Private constructor. 
    private Contact2(string contactName, string contactAddress)
    {
      Name = contactName;
      Address = contactAddress;        
    }

    // Public factory method. 
    public static Contact2 CreateContact(string name, string address)
    {
      return new Contact2(name, address);
    }
  }

  public class Program
  { 
    static void Main()
    {
      // Some simple data sources. 
      string[] names = {"Terry Adams","Fadi Fakhouri", "Hanying Feng", 
               "Cesar Garcia", "Debra Garcia"};
      string[] addresses = {"123 Main St.", "345 Cypress Ave.", "678 1st Ave",
                 "12 108th St.", "89 E. 42nd St."};

      // Simple query to demonstrate object creation in select clause. 
      // Create Contact objects by using a constructor. 
      var query1 = from i in Enumerable.Range(0, 5)
            select new Contact(names[i], addresses[i]);

      // List elements cannot be modified by client code. 
      var list = query1.ToList();
      foreach (var contact in list)
      {
        Console.WriteLine("{0}, {1}", contact.Name, contact.Address);
      }

      // Create Contact2 objects by using a static factory method. 
      var query2 = from i in Enumerable.Range(0, 5)
             select Contact2.CreateContact(names[i], addresses[i]);

      // Console output is identical to query1. 
      var list2 = query2.ToList();

      // List elements cannot be modified by client code. 
      // CS0272: 
      // list2[0].Name = "Eugene Zabokritski"; 

      // Keep the console open in debug mode.
      Console.WriteLine("Press any key to exit.");
      Console.ReadKey();        
    }
  }

								 
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