索引器的自定义使用[]

这实际上与编写一个典型的属性几乎相同:

public class MySessionThing
{
    public object this[string key]
    {
        //called when we ask for something = mySession["value"]
        get
        {
            return MyGetData(key);
        }
        //called when we assign mySession["value"] = something
        set
        {
            MySetData(key, value);
        }
    }

    private object MyGetData(string key)
    {
        //lookup and return object
    }

    private void MySetData(string key, object value)
    {
        //store the key/object pair to your repository
    }
}

唯一的区别是我们使用关键字“this”而不是给它一个合适的名称:

public          object            MyProperty
^access         ^(return) type    ^name
 modifier

public          object            this
^ditto          ^ditto            ^ "name"

MSDN documentation :

class SampleCollection<T>
{
    // Declare an array to store the data elements.
    private T[] arr = new T[100];

    // Define the indexer, which will allow client code
    // to use [] notation on the class instance itself.
    // (See line 2 of code in Main below.)        
    public T this[int i]
    {
        get
        {
            // This indexer is very simple, and just returns or sets
            // the corresponding element from the internal array.
            return arr[i];
        }
        set
        {
            arr[i] = value;
        }
    }
}

// This class shows how client code uses the indexer.
class Program
{
    static void Main(string[] args)
    {
        // Declare an instance of the SampleCollection type.
        SampleCollection<string> stringCollection = new SampleCollection<string>();

        // Use [] notation on the type.
        stringCollection[0] = "Hello, World";
        System.Console.WriteLine(stringCollection[0]);
    }
}

C#中的索引器是具有以下名称的属性 this 这里有一个例子。..

public class Session {
   //...
   public string this[string key]
   {
      get { /* get it from the database */ }
      set { /* store it in the database */ }
   }
}

public class KeyValueIndexer<K,V>
{
    private Dictionary<K, V> myVal = new Dictionary<K, V>();

    public V this[K k]
    {
        get
        {
            return myVal[k];
        }
        set
        {
            myVal.Add( k, value );
        }
    }
}

class Person
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string MiddleName { get; set; }
}

 static void Main( string[] args )
        {
            KeyValueIndexer<string, object> _keyVal = new KeyValueIndexer<string, object>();
            _keyVal[ "Person" ] = new Person() { FirstName="Jon", LastName="Doe", MiddleName="S" };
            _keyVal[ "MyID" ] = 123;
            Console.WriteLine( "My name is {0} {1}, {2}", ( ( Person ) _keyVal   [ "Person" ] ).FirstName, ( ( Person ) _keyVal[ "Person" ] ).MiddleName, ( ( Person ) _keyVal[ "Person" ] ).LastName );
            Console.WriteLine( "My ID is {0}", ( ( int ) _keyVal[ "MyID" ] ) );
            Console.ReadLine();
        }

如果你想用你的类来控制ASP。NET会话状态,希望实现 SessionStateStoreProviderBase 类和 IRequiresSessionState

    <sessionState cookieless="true" regenerateExpiredSessionId="true" mode="Custom" customProvider="MySessionProvider">
        <providers>
            <add name="MySessionProvider" type="MySession.MySessionProvider"/>
        </providers>
    </sessionState>

我见过这种用于创建压缩/加密会话状态的技术。