C# - IList Example - Dot Net Perls

IList. In C# lists and arrays implement IList. This interface is an abstraction that allows list types to be used with through a single reference.

With IList, we can create a single method to receive an int array, or a List of ints. This is powerful—it allows us to combine and reuse code.

interface

List

Example. With IList, you must specify a type parameter. If you want your method to act upon ints, you can use IList int. Any type (string, object) can be specified.

Next In this program, we introduce the Display method, which receives an IList int parameter.

Detail The Display method accesses the Count property and then uses the enumerator in a foreach-loop.

Property

foreach

Info You can pass an int[] or a List int to the Display method. These are implicitly cast to their base interface IList int.

Note Arrays always implement IList T. The List type also implements IList T.

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); } } }

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

IEnumerable use. Consider this alternative program—it uses IEnumerable instead of IList. With IEnumerable we do not have a Count property.

IEnumerable

But We can use the Count() extension method from LINQ on an IEnumerable. This will return the same value.

Count

using System; using System.Collections.Generic; class Program { static void Main() { Display(new int[] {1, 2}); Display(new List<int>() {1, 2}); } static void Display(IEnumerable<int> list) { foreach (int value in list) { Console.WriteLine(value); } } }

1 2 1 2

Discussion. You can also implement IList T for a custom class. The methods required are an indexer, the IndexOf method, the Insert method, and the RemoveAt method.

Indexer

List Insert

List Remove

Summary. 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.

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This page was last updated on Feb 9, 2024 (edit).

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