C# - What is indexer? where it is used ?

[preethisingh]

What is indexer? where it is used ?

[dheerajindian]

Originally Posted by preethisingh

What is indexer? where it is used ?

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.

// cs_keyword_indexers.cs
using System;
class IndexerClass
{
private int [] myArray = new int[100];
public int this [int index]
// Indexer declaration
{
get
{
// Check the index limits.
if (index < 0 || index >= 100)
return 0;
else
return myArray[index];
}
set
{
if (!(index < 0 || index >= 100))
myArray[index] = value;
}
}
}


public class MainClass
{
public static void Main()
{
IndexerClass b = new IndexerClass();
// Call the indexer to initialize the elements #3 and #5.
b[3] = 256;
b[5] = 1024;
for (int i=0; i<=10; i++)
{
Console.WriteLine("Element #{0} = {1}", i, b[i]);
}
}
}

Output

Element #0 = 0
Element #1 = 0
Element #2 = 0
Element #3 = 256
Element #4 = 0
Element #5 = 1024
Element #6 = 0
Element #7 = 0
Element #8 = 0
Element #9 = 0
Element #10 = 0

Notice that when an indexer's access is evaluated (for example, in a Console.Write statement) the get accessor is invoked. Therefore, if no get accessor exists, a compile-time error occurs.

For More see : Indexer Declaration (C#)
Indexers Tutorial (C#)