C# | Creating a read-only wrapper for List
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:
// 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); } } |
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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:
Unhandled Exception:
System.NotSupportedException: Collection is read-only.
Reference:
