Why is ReadOnlyObservableCollection.CollectionChanged not public?

Question

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

What is the use of a col

Answer 1

This was top hit on google so I figured I'd add my solution in case other people look this up.

Using the information above (about needing to cast to INotifyCollectionChanged), I made two extension methods to register and unregister.

My Solution - Extension Methods

public static void RegisterCollectionChanged(this INotifyCollectionChanged collection, NotifyCollectionChangedEventHandler handler)
{
    collection.CollectionChanged += handler;
}

public static void UnregisterCollectionChanged(this INotifyCollectionChanged collection, NotifyCollectionChangedEventHandler handler)
{
    collection.CollectionChanged -= handler;
}

Example

IThing.cs

public interface IThing
{
    string Name { get; }
    ReadOnlyObservableCollection Values { get; }
}

Using the Extension Methods

public void AddThing(IThing thing)
{
    //...
    thing.Values.RegisterCollectionChanged(this.HandleThingCollectionChanged);
}

public void RemoveThing(IThing thing)
{
    //...
    thing.Values.UnregisterCollectionChanged(this.HandleThingCollectionChanged);
}

OP's Solution

public void AddThing(IThing thing)
{
    //...
    INotifyCollectionChanged thingCollection = thing.Values;
    thingCollection.CollectionChanged += this.HandleThingCollectionChanged;
}

public void RemoveThing(IThing thing)
{
    //...
    INotifyCollectionChanged thingCollection = thing.Values;
    thingCollection.CollectionChanged -= this.HandleThingCollectionChanged;
}

Alternative 2

public void AddThing(IThing thing)
{
    //...
    (thing.Values as INotifyCollectionChanged).CollectionChanged += this.HandleThingCollectionChanged;
}

public void RemoveThing(IThing thing)
{
    //...
    (thing.Values as INotifyCollectionChanged).CollectionChanged -= this.HandleThingCollectionChanged;
}