Convert ArrayList, List

In the C# programming language, an ArrayList can be converted into a List. This can be done in a variety of ways.

One conversion approach uses the extension method syntax. This syntax gives us an effective ToList method for the ArrayList type.

This program introduces the static Extensions class and the ToList generic method inside that class. ToList is a generic extension method—it has a type parameter.

using System;
using System.Collections;
using System.Collections.Generic;

static class Extensions
{
    /// <summary>
    /// Convert ArrayList to List.
    /// </summary>
    public static List<T> ToList<T>(this ArrayList arrayList)
    {
        List<T> list = new List<T>(arrayList.Count);
        foreach (T instance in arrayList)
        {
            list.Add(instance);
        }
        return list;
    }
}

class Program
{
    static void Main()
    {
        // Create ArrayList.
        ArrayList arrayList = new ArrayList();
        arrayList.Add(1);
        arrayList.Add(2);
        arrayList.Add(3);

        // Use extension method.
        List<int> list = arrayList.ToList<int>();
        foreach (int value in list)
        {
            Console.WriteLine(value);
        }
    }
}
1
2
3

Notes, testing

I also tested the method using string literals in the ArrayList and it worked correctly. Just change the type of the local variables in the program.

With ToList we converted an ArrayList to a List. Another approach is to convert the ArrayList to an Array, and then use the new List constructor with that Array as the parameter.