October 17, 2021

Programmingempire

This article explains One Dimensional and Two Dimensional Indexers in C#. In short, an indexer allows an object to behave like an array.

What is an Indexer?

Basically, an indexer is a member of a class in C#. The following list provides important points regarding an indexer.

Since, indexers are members of a class, they are accessible using the objects of the class.
Moreover, we can’t use static keyword with indexers. In other words, indexers are instance members.
We create indexers using this keyword followed by parameters specified in the square brackets.
Since, we can specify, parameters with indexers, therefore, the indexers can be overloaded.
Likewise, an indexer can have get and set accessors. Further, at least one of the get or set accessors must be specified. Both accessors can’t be omitted. However, it is valid to specify only get or set accessor.
Furthermore, it is not possible to specify access modifiers for both accessors. Still we can specify it for any one of the get and set accessor.
Also, the access modifier for get or set accessor must be more restrictive than the access modifier for the indexer itself. For instance, if the indexer is declared as protected, then get or set accessor can’t be declared as public.

Creating Indexers

To illustrate indexers, consider the following example.

class MyClass
{
     int[] a={1,2,3};
     //Creating Indexer
     public int[int i]
     {
          get{ 
                return a[i];
             }
          set{
                 a[i]=value;
             }
     }
}

The above example demonstrates a simple indexer that we can use to iterate over the array. In general, an indexer has the following syntax.

<access-modifier> <type> this[parameter-list]
{
    get{
          //statement
       }
    set{
          //statement
        }
}

Example Code to Demonstrate One Dimensional and Two Dimensional Indexers in C#

The following program implements One Dimensional and Two Dimensional Indexers in C#. As a matter of fact, when we create an object of the class, we can call the indexer by just using the index with the object name. In order, to call the set accessor we need to assign a value. For example, the statement, ob[i]=10; calls the set accessor. Similarly, for calling the get accessor, we just require to use the object with a specific index in any statement.

using System;
using System.Linq;

namespace IndexerDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //Demo of One-Dimensional Indexer
            MyClass ob = new MyClass();
            Console.WriteLine("Displaying Integer Array: ");
            for(int i=0;i<10;i++)
            {
                Console.Write(ob[i] + " ");
            }
            //Set the values using Indexer
            for (int i = 0; i < 10; i++)
            {
                ob[i] = i * (i + 1);
            }
            Console.WriteLine("After Changing Values...");
            for (int i = 0; i < 10; i++)
            {
                Console.Write(ob[i] + " ");
            }
            Console.WriteLine("\n\n");
            //Demo of Multi-Dimensional Indexer
            Console.WriteLine("Illustration of Two Dimensional Indexer.");
            Console.WriteLine("A random string is appended in each element of String array.");
            Console.WriteLine("The index and random string are passed as parameters of the indexer.\n");
            for (int i=0;i<10;i++)
            {
                //Randomly Generate a String
                String s = "";
                Random r = new Random();
                int n = r.Next(97, 122);
                s = s + (char)n;
                n = r.Next(97, 122);
                s = s + (char)n;
                n = r.Next(97, 122);
                s = s + (char)n;

                //Displaying String array using indexer
                Console.Write(ob[i, s] + " ");
            }
            Console.WriteLine("\n\n");
        }
    }
    class MyClass
    {
        int[] arr = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
        String[] sarr = {"ab", "bc", "cd", "de", "ef", "fg", "gh", "hi", "ij", "jk" };
        //One-Dimensional Indexer
        public int this[int i]
        {
            get
            {
                return arr[i];
            }
            set
            {
                arr[i] = value;
            }
        }


         //Multi-Dimensional Indexer
        public String this[int a, String s]
        {
            get
            {
                sarr[a] = String.Join(':', new String[] {sarr[a], s});
                return sarr[a];
            }
         }
    }

}

Output

Programmingempire

What is an Indexer?

Creating Indexers

Example Code to Demonstrate One Dimensional and Two Dimensional Indexers in C#

Further Reading

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