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    <p>I'm posting my workaround - which is a custom class - here. Still hoping for better answers.</p> <pre><code>using System; using System.Collections; using System.Collections.Generic; using System.Collections.ObjectModel; using System.Collections.Specialized; using System.Linq; namespace ViewLayer { public class TransformObservableCollection&lt;T,Source&gt; : INotifyCollectionChanged, IList, IReadOnlyList&lt;T&gt;, IDisposable { public TransformObservableCollection(ObservableCollection&lt;Source&gt; wrappedCollection, Func&lt;Source,T&gt; transform) { m_WrappedCollection = wrappedCollection; m_TransformFunc = transform; ((INotifyCollectionChanged)m_WrappedCollection).CollectionChanged += TransformObservableCollection_CollectionChanged; m_TransformedCollection = new ObservableCollection&lt;T&gt;(m_WrappedCollection.Select(m_TransformFunc)); } public void Dispose() { if (m_WrappedCollection == null) return; ((INotifyCollectionChanged)m_WrappedCollection).CollectionChanged -= TransformObservableCollection_CollectionChanged; m_WrappedCollection = null; } void TransformObservableCollection_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e) { switch (e.Action) { case NotifyCollectionChangedAction.Add: if (e.NewItems == null || e.NewItems.Count != 1) break; m_TransformedCollection.Insert(e.NewStartingIndex,m_TransformFunc((Source)e.NewItems[0])); return; case NotifyCollectionChangedAction.Move: if (e.NewItems == null || e.NewItems.Count != 1 || e.OldItems == null || e.OldItems.Count != 1) break; m_TransformedCollection.Move(e.OldStartingIndex, e.NewStartingIndex); return; case NotifyCollectionChangedAction.Remove: if (e.OldItems == null || e.OldItems.Count != 1) break; m_TransformedCollection.RemoveAt(e.OldStartingIndex); return; case NotifyCollectionChangedAction.Replace: if (e.NewItems == null || e.NewItems.Count != 1 || e.OldItems == null || e.OldItems.Count != 1 || e.OldStartingIndex != e.NewStartingIndex) break; m_TransformedCollection[e.OldStartingIndex] = m_TransformFunc((Source)e.NewItems[0]); return; } // This is most likely called on a Clear(), we don't optimize the other cases (yet) m_TransformedCollection.Clear(); foreach (var item in m_WrappedCollection) m_TransformedCollection.Add(m_TransformFunc(item)); } #region IList Edit functions that are unsupported because this collection is read only public int Add(object value) { throw new InvalidOperationException(); } public void Clear() { throw new InvalidOperationException(); } public void Insert(int index, object value) { throw new InvalidOperationException(); } public void Remove(object value) { throw new InvalidOperationException(); } public void RemoveAt(int index) { throw new InvalidOperationException(); } #endregion IList Edit functions that are unsupported because this collection is read only #region Accessors public T this[int index] { get { return m_TransformedCollection[index]; } } object IList.this[int index] { get { return m_TransformedCollection[index]; } set { throw new InvalidOperationException(); } } public bool Contains(T value) { return m_TransformedCollection.Contains(value); } bool IList.Contains(object value) { return ((IList)m_TransformedCollection).Contains(value); } public int IndexOf(T value) { return m_TransformedCollection.IndexOf(value); } int IList.IndexOf(object value) { return ((IList)m_TransformedCollection).IndexOf(value); } public int Count { get { return m_TransformedCollection.Count; } } public IEnumerator&lt;T&gt; GetEnumerator() { return m_TransformedCollection.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return ((IEnumerable)m_TransformedCollection).GetEnumerator(); } #endregion Accessors public bool IsFixedSize { get { return false; } } public bool IsReadOnly { get { return true; } } public void CopyTo(Array array, int index) { ((IList)m_TransformedCollection).CopyTo(array, index); } public void CopyTo(T[] array, int index) { m_TransformedCollection.CopyTo(array, index); } public bool IsSynchronized { get { return false; } } public object SyncRoot { get { return m_TransformedCollection; } } ObservableCollection&lt;T&gt; m_TransformedCollection; ObservableCollection&lt;Source&gt; m_WrappedCollection; Func&lt;Source, T&gt; m_TransformFunc; event NotifyCollectionChangedEventHandler INotifyCollectionChanged.CollectionChanged { add { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged += value; } remove { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged -= value; } } } } </code></pre>
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    1. COI still don't see the need to do this. If you want something to be read-only, don't write code that modifies it, and you're done. I don't see how it makes sense to you to expose a read only collection that wraps a non read only one. Unless you're letting your UI elements manipulate the bound collection by adding or removing items from it, which is something I recommend against.
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    2. CONot sure if I get you right, but you seem to refer to 2 very different issues. First is the need for a collection that mirrors another collection but does an element-by-element transform, second is the fact that I make a collection that would break if the user changed it directly read only. The reason for the first is that in many cases in MVVM where the Models expose containers of items, an element-by-element projection of those containers is required in the View Model.
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    3. COYep I understand the first, but the second?
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