.NET Framework ReadOnlyCollections Updating a ReadOnlyCollection
Example
A ReadOnlyCollection cannot be edited directly. Instead, the source collection is updated and the ReadOnlyCollection will reflect these changes. This is the key feature of the ReadOnlyCollection.
var groceryList = new List<string> { "Apple", "Banana" };
var readOnlyGroceryList = new ReadOnlyCollection<string>(groceryList);
var itemCount = readOnlyGroceryList.Count; // There are currently 2 items
//readOnlyGroceryList.Add("Candy"); // Compiler Error - Items cannot be added to a ReadOnlyCollection object
groceryList.Add("Vitamins"); // ..but they can be added to the original collection
itemCount = readOnlyGroceryList.Count; // Now there are 3 items
var lastItem = readOnlyGroceryList.Last(); // The last item on the read only list is now "Vitamins"
