Description
C# Indexers are called as smart arrays which allow an instance of class or struct to be indexed like an array or virtual array. Representation of indexers is same as properties and modifier can be private, public, protected or internal.
Syntax
this[argument list]
{
get
{
//Return the value
}
set
{
//set the values
}
}
Example
[csharp]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace SPLessons
{
class Program
{
static void Main(string[] args)
{
SampleCollection<string> stringCollection = new SampleCollection<string>();
stringCollection[0] = "Hello World";
stringCollection[1] = "Welcome";
stringCollection[2] = "Good Noon!";
for (int i = 0; i < 3; i++)
{
System.Console.WriteLine(stringCollection[i]);
}
}
class SampleCollection<T>
{
private string[] arr = new string[100];
// Define the indexer, which will allow client code
public string 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;
}
}
}
}
}
[/csharp]
Output:
Note
- this is used to define the indexers.
- value keyword is used to set value.
- Indexers can be overloaded.
Description
Overloaded Indexers can be used with multiple parameter and overloading is also possible on indexers.
Example
[csharp]
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace OverLoadingIndexer
{
class Friends
{
private string[] Member; // Private data member, its an array
public Friends(int n)
{
Member = new string[n];
for (int i = 0; i < n; i++)
Member[i] = "empty";
}
public string this[int i] //Its an indexer and looks like property definition
{
set
{
Member[i] = value;
}
get
{
return Member[i];
}
}
public string this[string item] //Indexer Overlading with string in the place of index position and its a write only
{
set
{
for (int i = 0; i < Member.Length; i++)
{
if (Member[i] == item)
{
Member[i] = value;
break;
}
}
}
}
public void Show() // display the contents of array
{
for (int i = 0; i < Member.Length; i++)
Console.WriteLine(Member[i]);
Console.WriteLine();
}
}
class Program
{
static void Main(string[] args)
{
Friends FriendsofJames = new Friends(2);
//Following statements are used to assign different names to "FriendsofJohn" Object
FriendsofJames[0] = "John"; // Object behaves like an array
FriendsofJames[1] = "Mark";
Console.WriteLine("Friends list of John :");
FriendsofJames.Show();
//We could change/modify the content using friendname instead of index position
FriendsofJames["Bharat"] = "Bharat"; // invokes indexer with string parameter
FriendsofJames["Kumar"] = "Kumar";
Console.WriteLine("Friends list after update");
FriendsofJames.Show();
}
}
}
[/csharp]
Output:
