HOW TO：使用自動實作的屬性來實作輕量型類別 (C# 程式設計手冊)
本範例顯示如何建立不變的、輕量型類別，該類別只提供封裝自動實作屬性集的服務。 使用這種建構而非必須使用參考型別語意時的結構 (Struct)。
請注意，使用自動實作屬性時，會同時需要 get 與 set 這兩個存取子。 如果要將類別設定為不變的，請將 set 存取子宣告為 private。 不過，當您宣告私用 set 存取子時，不能夠使用物件初始設定式來初始化屬性。 必須使用建構函式或 Factory 方法。
範例
下列範例示範兩種方法，教您如何實作具有自動實作屬性的不可變類別。 第一個類別使用建構函式來初始化屬性，而第二個類別使用靜 Factory 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; private set; }
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 set; }
// 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();
}
}
/* Output:
Terry Adams, 123 Main St.
Fadi Fakhouri, 345 Cypress Ave.
Hanying Feng, 678 1st Ave
Cesar Garcia, 12 108th St.
Debra Garcia, 89 E. 42nd St.
*/
編譯器會對每個自動實作屬性建立支援欄位。 這些欄位無法從來源程式碼直接存取。