C# ArrayList with Examples

How to use ArrayList in C#?

In this article, you will learn how to use ArrayList in C#. ArrayList is a collection of variable-length arrays. I will show you how to initialize, add, delete, sort, and remove duplicates.

Learn more:

ArrayList initialization

This section shows how to initialize an ArrayList in C#.

You can initialize an ArrayList object as follows:

ArrayList list = new ArrayList();

Or:

 ArrayList list = new ArrayList()
 {
      "Apple", "Orange", "Grape"
 };

Adding elements

This section shows how to add elements to an ArrayList in C#.

To add a new element to an ArrayList, use the Add() method.

ArrayList list = new ArrayList();
list.Add("Apple");
list.Add("Grape");

Sample code:

using System;
using System.Collections;
namespace CSharpExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize
            ArrayList list = new ArrayList()
            {
                "Apple", "Orange", "Grape", "Pineapple"
            };
            //Print
            Print(list);
            //Add elements
            list.Add("Orange");
            list.Add("Apple");
            Console.WriteLine("*********************");
            Console.WriteLine("After adding elements:");
            Print(list);
        }
        static void Print(ArrayList list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
    }
}

Output:

Element: Apple
Element: Orange
Element: Grape
Element: Pineapple
*********************
After adding elements:
Element: Apple
Element: Orange
Element: Grape
Element: Pineapple
Element: Orange
Element: Apple

Deleting elements

This section shows how to delete and add ArrayList in C#.

To delete elements from an ArrayList, use the Remove() or RemoveAt() method.

//Initialize
ArrayList list = new ArrayList()
{
    "Apple", "Orange", "Grape"
};
//Delete using the Remove() method 
list.Remove("Orange");
//Delete using the RemoveAt() method
list.RemoveAt(0);

Sample code:

using System;
using System.Collections;
namespace CSharpExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize
            ArrayList list = new ArrayList()
            {
                "Apple", "Orange", "Grape", "Pineapple", "Melon", "Watermelon"
            };
            //Print
            Print(list);
            list.RemoveAt(0);
            list.Remove("Pineapple");
            list.Remove("Orange");
            Console.WriteLine("*********************");
            Console.WriteLine("After removing elements:");
            Print(list);
        }
        static void Print(ArrayList list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
    }
}

Output:

Element: Apple
Element: Orange
Element: Grape
Element: Pineapple
Element: Melon
Element: Watermelon
*********************
After removing elements:
Element: Grape
Element: Melon
Element: Watermelon

Sorting elements

This section shows how to sort elements of an ArrayList in C#.

To sort elements of an ArrayList in ascending order, use the Sort() method.

using System;
using System.Collections;
namespace CSharpExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize
            ArrayList list = new ArrayList()
            {
                "Apple", "Orange", "Grape", "Melon"
            };
            //Print
            Print(list);
            //Sort
            list.Sort();
            Console.WriteLine("***********************");
            Console.WriteLine("Sorting in ascending order:");
            //Print
            Print(list);
        }
        static void Print(ArrayList list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
    }
}

Output:

Element: Apple
Element: Orange
Element: Grape
Element: Melon
***********************
Sorting in ascending order:
Element: Apple
Element: Grape
Element: Melon
Element: Orange

To order the elements of an ArrayList in descending order, use the Sort() and Reverse() methods.

using System;
using System.Collections;
namespace CSharpExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize
            ArrayList list = new ArrayList()
            {
                "Apple", "Orange", "Pineapple", "Grape", "Melon"
            };
            //Print
            Print(list);
            //Sort
            list.Sort();
            Console.WriteLine("***********************");
            Console.WriteLine("Sorting in descending order:");
            //Reverse
            list.Reverse();
            //Print
            Print(list);
        }
        static void Print(ArrayList list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
    }
}

Output:

lement: Apple
Element: Orange
Element: Pineapple
Element: Grape
Element: Melon
***********************
Sorting in descending order:
Element: Pineapple
Element: Orange
Element: Melon
Element: Grape
Element: Apple

Removing duplicate elements

Learn how to remove duplicate elements in an ArrayList in C#.

To remove duplicates from an ArrayList, you can use Linq's Distinct() as shown in the sample code below.

using System;
using System.Collections;
using System.Linq;
namespace CSharpExample
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initialize
            ArrayList list = new ArrayList()
            {
                "Apple", "Orange", "Pineapple", "Grape",
                "Melon", "Orange", "Apple", "Grape"
            };
            //Print
            Print(list);
            Console.WriteLine("***********************");
            Console.WriteLine("Removing duplicates:");
            IEnumerable<object> list2 = list.Cast<object>().Distinct();
            //Print
            Print2(list2);
        }
        static void Print(ArrayList list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
        static void Print2(IEnumerable<object> list)
        {
            foreach (object element in list)
            {
                Console.WriteLine("Element: {0}", element);
            }
        }
    }
}

Output:

Element: Apple
Element: Orange
Element: Pineapple
Element: Grape
Element: Melon
Element: Orange
Element: Apple
Element: Grape
***********************
Removing duplicates:
Element: Apple
Element: Grape
Element: Melon
Element: Orange
Element: Pineapple

Summary

I hope you enjoyed this explanation of how to use ArrayList in C#, which is a collection of variable-length arrays. I have shown you how to initialize, add, delete, sort ArrayList.