ReadOnlyCollection in CSharp

Introduction

ReadOnlyCollection<T> is a collection which wrap List<T> and do not allow any modification in it.

Any modification in List<T> will be reflected to the ReadOnlyCollection<T>.

We can present ReadOnlyCollection as below

ReadOnlyCollection<T> readonlyvar=new ReadOnlyCollection<T>(<Collection Object>);

Description

To Understand ReadOnlyCollection we need to take an example.

Take a list of Student Roll number.

List<int> list = new List<int>();
list.Add(1);
list.Add(3);
list.Add(5);

Take ReadOnlyCollection which wrap List object.

ReadOnlyCollection<int> readonlyvar=new ReadOnlyCollection<int>(list);

Try to print element from ReadOnlyCollection .

foreach(int i in readonlyvar)
{
Console.WriteLine(i + " ");
}

After that Insert a value in the middle of the list.

list.Insert(1, 6);

Again try to print the ReadOnlyCollection.

foreach (int i in readonlyvar)
{

Console.WriteLine(i + " " );
}

Below is the complete program which explain ReadOnlyCollection.

public static void Main()
{
//Can change to the list
List<int> list = new List<int>();
list.Add(1);
list.Add(3);
list.Add(5);
//can not change to the collection
ReadOnlyCollection<int> readonlyvar=new ReadOnlyCollection<int>(list);
foreach(int i in readonlyvar)
{
Console.WriteLine(i + " ");
}
Console.WriteLine("------------------------------------");
//Any changes to the list will reflect to ReadOnlyColection //as below
list.Insert(1, 6);

foreach (int i in readonlyvar)
{

Console.WriteLine(i + " " );
}
Console.ReadKey();
}

Out-Put

Why We Need ReadOnlyCollection

Readonlycollection stop allowing to modify the collection.
It improve the performance of the application.