Read-Only and Unmodifiable List in C#

This post will discuss how to read-only, immutable, unmodifiable List in C#.

To get a read-only view of a list, we can use the ReadOnlyCollection<T> class. The following code example demonstrates its usage. It creates a List<T> of integers and then wraps the list in a ReadOnlyCollection<T>.

using System;

using System.Collections.ObjectModel;

using System.Collections.Generic;

public class Example

{

public static void Main()

{

List<int> nums = new List<int>() { 1, 2, 3, 4, 5 };

ReadOnlyCollection<int> immutableList = new ReadOnlyCollection<int>(nums);

Console.WriteLine(String.Join(", ", immutableList)); // 1, 2, 3, 4, 5

}

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Note that the ReadOnlyCollection<T> class is a read-only view over the specified list. Therefore, any changes made to the underlying list are reflected in the read-only list.

Alternatively, you can use the List<T>.AsReadOnly() convenience method to get a read-only IList<T> generic interface implementation that wraps the original list.