How can I make a read-only ObservableCollection property?

Question

I\'d like to expose a property on a view model that contains a list of objects (from database).

I need this collection to be read-only. That is, I want to prevent A

Answer 1

The [previously] accepted answer will actually return a different ReadOnlyObservableCollection every time ReadOnlyFoo is accessed. This is wasteful and can lead to subtle bugs.

A preferable solution is:

public class Source
{
    Source()
    {
        m_collection = new ObservableCollection();
        m_collectionReadOnly = new ReadOnlyObservableCollection(m_collection);
    }
 
    public ReadOnlyObservableCollection Items
    {
        get { return m_collectionReadOnly; }
    }
 
    readonly ObservableCollection m_collection;
    readonly ReadOnlyObservableCollection m_collectionReadOnly;
}

See ReadOnlyObservableCollection anti-pattern for a full discussion.