C# IList

Lists and arrays implement IList. This interface is an abstraction that allows list types to be used with through a single reference type. With it, we can create a single method to receive an int[] or a List<int>.

Example

First, with the IList generic interface, you must specify a type parameter. If you want your method to act upon ints, you can use IList<int>.

In this program, we introduce the Display method, which receives an IList<int> parameter. It accesses the Count property and then uses the enumerator in a foreach-loop.

Int TypeForeach Loop Examples

Program that uses IList<T> generic interface [C#]

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
	int[] array = new int[3];
	array[0] = 1;
	array[1] = 2;
	array[2] = 3;
	Display(array);

	List<int> list = new List<int>();
	list.Add(5);
	list.Add(7);
	list.Add(9);
	Display(list);
    }

    static void Display(IList<int> list)
    {
	Console.WriteLine("Count: {0}", list.Count);
	foreach (int value in list)
	{
	    Console.WriteLine(value);
	}
    }
}

Output

Count: 3
1
2
3
Count: 3
5
7
9

Passing collections to Display method.You can see in the Main method that you can pass an int[] or a List<int> to the Display method. These are implicitly cast to their base interface IList<int>. Arrays always implement IList<T>. The List type also implements IList<T>.

Array TypesList Examples

Implement IList<T>

You can also implement IList<T> for a custom class in your C# program. The methods required by this contract are an indexer; the IndexOf method; the Insert method; and the RemoveAt method.

Indexer Examples

Summary

In this article, we looked at the IList generic interface, which can be used as an abstraction for arrays and Lists. The IList generic interface is separate from the regular IList interface.

Note:With this layer of abstraction, you can formulate more concise ways of acting upon your data.