ObservableCollection element-wise Transform/Projection Wrapper

Question

When creating ViewModels in WPF it\'s sometimes necessary to transform data that is available in an ObservableCollection (the source collection) into a collection of wrapper

Answer 1

I'm posting my workaround - which is a custom class - here. Still hoping for better answers.

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<T,Source> : INotifyCollectionChanged, IList, IReadOnlyList<T>, IDisposable
    {
        public TransformObservableCollection(ObservableCollection<Source> wrappedCollection, Func<Source,T> transform)
        {
            m_WrappedCollection = wrappedCollection;
            m_TransformFunc = transform;
            ((INotifyCollectionChanged)m_WrappedCollection).CollectionChanged += TransformObservableCollection_CollectionChanged;
            m_TransformedCollection = new ObservableCollection<T>(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<T> 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<T> m_TransformedCollection;
        ObservableCollection<Source> m_WrappedCollection;
        Func<Source, T> m_TransformFunc;

        event NotifyCollectionChangedEventHandler INotifyCollectionChanged.CollectionChanged
        {
            add { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged += value; }
            remove { ((INotifyCollectionChanged)m_TransformedCollection).CollectionChanged -= value; }
        }
    }
}