Csharp 简明教程

C

indexer 允许对一个对象进行索引，例如一个数组。当你为一个类定义一个索引器时，该类表现类似于一个 virtual array 。然后你可以使用数组访问运算符（[ ]）访问该类的实例。

An indexer allows an object to be indexed such as an array. When you define an indexer for a class, this class behaves similar to a virtual array. You can then access the instance of this class using the array access operator ([ ]).

Syntax

一维索引器具有以下语法 -

A one dimensional indexer has the following syntax −

element-type this[int index] {

   // The get accessor.
   get {
      // return the value specified by index
   }

   // The set accessor.
   set {
      // set the value specified by index
   }
}

Use of Indexers

索引器的行为声明在某种程度上类似于属性。类似于属性，你使用 get 和 set 访问器来定义一个索引器。然而，属性返回或设置一个特定的数据成员，而索引器返回或设置对象实例中的一个特定值。换句话说，它将实例数据分解成更小的部分并对每个部分进行编制索引，获取或设置每个部分。

Declaration of behavior of an indexer is to some extent similar to a property. similar to the properties, you use * get* and set accessors for defining an indexer. However, properties return or set a specific data member, whereas indexers returns or sets a particular value from the object instance. In other words, it breaks the instance data into smaller parts and indexes each part, gets or sets each part.

定义一个属性涉及提供一个属性名称。索引器不是使用名称进行定义的，而是使用 this 关键字，该关键字引用对象实例。以下示例演示此概念 −

Defining a property involves providing a property name. Indexers are not defined with names, but with the this keyword, which refers to the object instance. The following example demonstrates the concept −

using System;

namespace IndexerApplication {

   class IndexedNames {
      private string[] namelist = new string[size];
      static public int size = 10;

      public IndexedNames() {
         for (int i = 0; i < size; i++)
         namelist[i] = "N. A.";
      }
      public string this[int index] {
         get {
            string tmp;

            if( index >= 0 && index <= size-1 ) {
               tmp = namelist[index];
            } else {
               tmp = "";
            }

            return ( tmp );
         }
         set {
            if( index >= 0 && index <= size-1 ) {
               namelist[index] = value;
            }
         }
      }
      static void Main(string[] args) {
         IndexedNames names = new IndexedNames();
         names[0] = "Zara";
         names[1] = "Riz";
         names[2] = "Nuha";
         names[3] = "Asif";
         names[4] = "Davinder";
         names[5] = "Sunil";
         names[6] = "Rubic";

         for ( int i = 0; i < IndexedNames.size; i++ ) {
            Console.WriteLine(names[i]);
         }
         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Zara
Riz
Nuha
Asif
Davinder
Sunil
Rubic
N. A.
N. A.
N. A.

Overloaded Indexers

索引器可以进行重载。索引器还可以使用多个参数进行声明，每个参数都可以是不同的类型。索引不必是整数。C# 允许索引为其他类型，例如字符串。

Indexers can be overloaded. Indexers can also be declared with multiple parameters and each parameter may be a different type. It is not necessary that the indexes have to be integers. C# allows indexes to be of other types, for example, a string.

以下示例演示重载索引器 −

The following example demonstrates overloaded indexers −

using System;

namespace IndexerApplication {
   class IndexedNames {
      private string[] namelist = new string[size];
      static public int size = 10;

      public IndexedNames() {
         for (int i = 0; i < size; i++) {
            namelist[i] = "N. A.";
         }
      }
      public string this[int index] {
         get {
            string tmp;

            if( index >= 0 && index <= size-1 ) {
               tmp = namelist[index];
            } else {
               tmp = "";
            }

            return ( tmp );
         }
         set {
            if( index >= 0 && index <= size-1 ) {
               namelist[index] = value;
            }
         }
      }

      public int this[string name] {
         get {
            int index = 0;

            while(index < size) {
               if (namelist[index] == name) {
                return index;
               }
               index++;
            }
            return index;
         }
      }

      static void Main(string[] args) {
         IndexedNames names = new IndexedNames();
         names[0] = "Zara";
         names[1] = "Riz";
         names[2] = "Nuha";
         names[3] = "Asif";
         names[4] = "Davinder";
         names[5] = "Sunil";
         names[6] = "Rubic";

         //using the first indexer with int parameter
         for (int i = 0; i < IndexedNames.size; i++) {
            Console.WriteLine(names[i]);
         }

         //using the second indexer with the string parameter
         Console.WriteLine(names["Nuha"]);
         Console.ReadKey();
      }
   }
}

编译并执行上述代码后，将产生以下结果 −

When the above code is compiled and executed, it produces the following result −

Zara
Riz
Nuha
Asif
Davinder
Sunil
Rubic
N. A.
N. A.
N. A.
2