Array.AsReadOnly(T[]) Method in C#

The Array.AsReadOnly(T[]) method in C# returns a read-only wrapper for the specified array, which is the read-only ReadOnlyCollection<T>.

Syntax

public static System.Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly<T> (T[] array);

Here, T is the type of the elements of the array, whereas array T[] is the one-dimensional zero-based array.

Let us now see an example to implement the Array.AsReadOnly(T[]) method −

Example

using System;
using System.Collections.Generic;
public class Demo {
   public static void Main() {
      String[] arr = { "John", "Tom", "Katie", "Brad" };
      // read-only IList wrapper
      IList<String> list = Array.AsReadOnly( arr );
      // Display the values of the read-only IList.
      Console.WriteLine( "Initial read-only IList..." );
      display( list );
      // Let us now change the read-only wrapper
      try {
         list[0] = "Kevin";
         list[1] = "Bradley";
      }
      catch ( NotSupportedException e ) {
         Console.WriteLine(e.GetType());
         Console.WriteLine(e.Message );
         Console.WriteLine();
      }
      Console.WriteLine( "After changing two elements, the IList remains the same since it is read-only..." );
      display( list );
   }
   public static void display( IList<String> list ) {
      for ( int i = 0; i < list.Count; i++ ) {
         Console.WriteLine(list[i] );
      }
      Console.WriteLine();
   }
}

Output

This will produce the following output −

Initial read-only IList...
John
Tom
Katie
Brad
System.NotSupportedException
Collection is read-only.
After changing two elements, tthe IList remains the same since it is read-only...
John
Tom
Katie
Brad