How to Convert List<string> to ReadOnlyCollection<string> in C#

Question

I want to convert the items entered to a String list to:

System.Collections.ObjectModel.ReadOnlyCollection<string> 

I have tried using:

(System.Collections.ObjectModel.ReadOnlyCollection<string>)listname 

But it returns an error.

Answer 1

You can create a new instance using the existing List in the constructor.

var readOnlyList = new ReadOnlyCollection<string>(existingList); 

ReadOnlyCollection(Of T) Constructor on MSDN

Answer 2

If you've got:

List<string> names=new List<string>(){"Rod", "Jane", "Freddy"};

Then you can say:

ReadOnlyCollection<string> readOnlyNames=names.AsReadOnly();

This doesn't copy the list. Instead the readonly collection stores a reference to the original list and prohibits changing it. However, if you modify the underlying list via names then the readOnlyNames will also change, so it's best to discard the writable instance if you can.