Why is ReadOnlyObservableCollection.CollectionChanged not public?

Why is ReadOnlyObservableCollection.CollectionChanged protected and not public (as the corresponding ObservableCollection.CollectionChanged is)?

What is the use of a collection implementing INotifyCollectionChanged if I can't access the CollectionChanged event?

Here's the solution: CollectionChanged events on ReadOnlyObservableCollection

You have to cast the collection to INotifyCollectionChanged.

I've found a way for you of how to do this:

ObservableCollection<string> obsCollection = new ObservableCollection<string>();
INotifyCollectionChanged collection = new ReadOnlyObservableCollection<string>(obsCollection);
collection.CollectionChanged += new NotifyCollectionChangedEventHandler(collection_CollectionChanged);

You just need to refer to your collection explicitly by INotifyCollectionChanged interface.

I know this post is old, however, people should take their time to understand the patterns used in .NET before commenting. A read only collection is a wrapper on an existing collection that prevents consumers from modifying it directly, look at ReadOnlyCollection and you will see that it is a wrapper on a IList<T> which may or may not be mutable. Immutable collections are a different matter and are covered by the new immutable collections library

In other words, read only is not the same as immutable!!!!

That aside, ReadOnlyObservableCollection should implicitly implement INotifyCollectionChanged.

There are definitely good reasons for wanting to subscribe to collection changed notifications on a ReadOnlyObservableCollection. So, as an alternative to merely casting your collection as INotifyCollectionChanged, if you happen to be subclassing ReadOnlyObservableCollection, then the following provides a more syntactically convenient way to access the a CollectionChanged event:

    public class ReadOnlyObservableCollectionWithCollectionChangeNotifications<T> : ReadOnlyObservableCollection<T>
{
    public ReadOnlyObservableCollectionWithCollectionChangeNotifications(ObservableCollection<T> list)
        : base(list)
    {
    }

    event System.Collections.Specialized.NotifyCollectionChangedEventHandler CollectionChanged2
    {
        add { CollectionChanged += value; }
        remove { CollectionChanged -= value; }
    }
}

This has worked well for me before.

You might vote for the bug entry on Microsoft Connect that describes this issue: https://connect.microsoft.com/VisualStudio/feedback/details/641395/readonlyobservablecollection-t-collectionchanged-event-should-be-public

Update:

The Connect portal has been shutdown by Microsoft. So the link above does not work anymore.

My Win Application Framework (WAF) library provides a solution: ReadOnlyObservableList class:

public class ReadOnlyObservableList<T> 
        : ReadOnlyObservableCollection<T>, IReadOnlyObservableList<T>
{
    public ReadOnlyObservableList(ObservableCollection<T> list)
        : base(list)
    {
    }

    public new event NotifyCollectionChangedEventHandler CollectionChanged
    {
        add { base.CollectionChanged += value; }
        remove { base.CollectionChanged -= value; }
    }

    public new event PropertyChangedEventHandler PropertyChanged
    {
        add { base.PropertyChanged += value; }
        remove { base.PropertyChanged -= value; }
    }
}