C# | Creating a read-only wrapper for the ArrayList

Last Updated : 01 Feb, 2019

ArrayList.ReadOnly(ArrayList) Method is used to get a read-only ArrayList wrapper. Syntax:

public static System.Collections.ArrayList ReadOnly(System.Collections.ArrayList list);

Here, the list is the ArrayList which is to be wrapped. Return Value: It returns a read-only ArrayList Wrapper around the list. Exception: This method returns the ArgumentNullException if the list is null. Below programs illustrate the use of above-discussed method: Example 1:

CSharp

// C# code to create a read-only // wrapper for the ArrayList using System; using System.Collections;  class GFG {      // Driver code     public static void Main()     {          // Creating an ArrayList         ArrayList myList = new ArrayList();          // Adding elements to ArrayList         myList.Add("Geeks");         myList.Add("for");         myList.Add("Geeks");         myList.Add("Noida");         myList.Add("Geeks Classes");         myList.Add("Delhi");          // Creating a Read-Only packing         // around the ArrayList         ArrayList myList2 = ArrayList.ReadOnly(myList);          // --------- Using IsReadOnly Property          // print the status of both ArrayList         Console.WriteLine("myList ArrayList is {0}.",                     myList.IsReadOnly ? "read-only" :                                      "not read-only");          Console.WriteLine("myList2 ArrayList is {0}.",                     myList2.IsReadOnly ? "read-only" :                                       "not read-only");     } }

Output:

  myList ArrayList is not read-only.  myList2 ArrayList is read-only.

Example 2:

CSharp

// C# code to create a read-only  // wrapper for the ArrayList using System;  using System.Collections;   class GFG {       // Driver code      public static void Main()      {           // Creating an ArrayList          ArrayList myList = new ArrayList();           // Adding elements to ArrayList          myList.Add("C");          myList.Add("C++");          myList.Add("Java");          myList.Add("C#");          myList.Add("Python");                   Console.WriteLine("Before Wrapping: ");                  // Displaying the elements in the ArrayList          foreach(string str in myList)          {              Console.WriteLine(str);          }                        // Creating a Read-Only packing          // around the ArrayList          ArrayList myList2 = ArrayList.ReadOnly(myList);                  Console.WriteLine("After Wrapping: ");                  // Displaying the elements          foreach(string str in myList2)          {              Console.WriteLine(str);          }                   Console.WriteLine("Trying to add new element into myList2:");                  // it will give error         myList2.Add("HTML");           }  }

Output:

  Before Wrapping:   C  C++  Java  C#  Python  After Wrapping:   C  C++  Java  C#  Python  Trying to add new element into myList2:

Runtime Error:

Unhandled Exception: System.NotSupportedException: Collection is read-only. at System.Collections.ArrayList+ReadOnlyArrayList.Add

Explanation: In the above program, you can add or remove the elements from the myList i.e original ArrayList which will reflect into the read-only collection. Note:

To prevent any modifications to list, expose list only through this wrapper.
A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection. If changes are made to the underlying collection, the read-only collection reflects those changes.
This method is an O(1) operation.

Reference:

https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.readonly?view=netframework-4.7.2#System_Collections_ArrayList_ReadOnly_System_Collections_ArrayList_

C# | Creating a read-only wrapper for the List

Kirti_Mangal

Improve

Article Tags :

C# | Creating a read-only wrapper for the ArrayList

Similar Reads