C# | Creating a read-only wrapper for List

Last Updated : 11 Jul, 2025

List<T>.AsReadOnly Method is used to get a read-only ReadOnlyCollection<T> wrapper for the current collection. Syntax:

public System.Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly ();

Return Value: It returns an object that acts as a read-only wrapper around the current List<T>. Example:

csharp

// C# code to create a read-only // wrapper for the List<T> using System; using System.Collections.Generic; class GFG {  // Driver code  public static void Main()  {  // Creating an List<T> of Integers  List<int> mylist = new List<int>();  // Adding elements to List  mylist.Add(17);  mylist.Add(19);  mylist.Add(21);  mylist.Add(9);  mylist.Add(75);  mylist.Add(19);  mylist.Add(73);  Console.WriteLine("Before Wrapping: ");  // Displaying the elements  // in the mylist  foreach(int i in mylist)  {  Console.WriteLine(i);  }  // Creating a Read-Only packing  // around the List  IList<int> readlist = mylist.AsReadOnly();  Console.WriteLine("After Wrapping: ");  // Displaying the elements  // of Read-Only Collection  foreach(int j in readlist)  {  Console.WriteLine(j);  }    // You can add elements to  // the original List i.e. mylist  Console.WriteLine("Adding new element to mylist: ");  mylist.Add(35);    // Displaying the elements  // in the mylist  foreach(int k in mylist)  {  Console.WriteLine(k);  }  // But you cannot add elements  // into the Read-Only Collection  Console.WriteLine("Trying to add new element into readlist:");  // it will give error  readlist.Add(34);    } }

Output:

 Before Wrapping: 17 19 21 9 75 19 73 After Wrapping: 17 19 21 9 75 19 73 Adding new element to mylist: 17 19 21 9 75 19 73 35 Trying to add new element into readlist:

Runtime Error: