Indexers permit instances of a class or struct to be indexed in the same way as arrays. Indexers are similar to properties except that their accessors take parameters.
In the following example, a generic class is defined and provided with simple get and set accessor methods as a means for assigning and retrieving values. The class Program creates an instance of this class for storing strings.
class SampleCollection<T>
{
private T[] arr = new T[100];
public T this[int i]
{
get
{
return arr[i];
}
set
{
arr[i] = value;
}
}
}
// This class shows how client code uses the indexer
class Program
{
static void Main(string[] args)
{
SampleCollection<string> stringCollection = new SampleCollection<string>();
stringCollection[0] = "Hello, World";
System.Console.WriteLine(stringCollection[0]);
}
}
-
Indexers enable objects to be indexed in a similar way to arrays.
-
A get accessor returns a value. A set accessor assigns a value.
-
The this keyword is used to define the indexers.
-
The value keyword is used to define the value being assigned by the set indexer.
-
Indexers do not have to be indexed by an integer value; it is up to you how to define the specific look-up mechanism.
-
Indexers can be overloaded.
-
Indexers can have more than one formal parameter, for example, when accessing a two-dimensional array.
C# Language Specification
For more information, see the following sections in the C# Language Specification:
Reference
Properties (C# Programming Guide)
Concepts
C# Programming Guide