Question

List (and List) instances can be readonly, seeing ReadOnly property; methods throws exceptions in the case the collection have the property ReadOnly property.

How can I create readonly List instances? What are the main uses?

Answer 1

ReadOnlyCollection

From the link above:

“A collection that is read-only is
simply a collection with a wrapper
that prevents modifying the
collection; therefore, if changes are
made to the underlying collection, the
read-only collection reflects those
changes.”

So, anytime you need a collection that is not changeable, use this.