public static IDisposable OnItems <TSource>(this INotifyCollectionChanged notifyingCollection, Func <TSource, IDisposable> onNewItem)
{
if (notifyingCollection == null)
{
throw new ArgumentNullException("notifyingCollection");
}
var collection = (ICollection)notifyingCollection;
var subscriptions = new Dictionary <TSource, IDisposable>();
var handleNewItem = new Action <TSource>(item => subscriptions.Add(item, onNewItem(item)));
var handleOldItem = new Action <TSource>(item =>
{
IDisposable subscription;
if (subscriptions.TryGetValue(item, out subscription))
{
subscriptions.Remove(item);
subscription.Dispose();
}
});
var handleDispose = new Action(() =>
{
foreach (var item in subscriptions.Keys.ToArray())
{
handleOldItem(item);
}
});
foreach (var item in collection.OfType <TSource>())
{
handleNewItem(item);
}
var collectionObservation = notifyingCollection.ObserveCollection()
.Subscribe(e =>
{
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
if (e.NewItems != null)
{
foreach (var item in e.NewItems.OfType <TSource>())
{
handleNewItem(item);
}
}
break;
case NotifyCollectionChangedAction.Remove:
if (e.OldItems != null)
{
foreach (var item in e.OldItems.OfType <TSource>())
{
handleOldItem(item);
}
}
break;
case NotifyCollectionChangedAction.Replace:
if (e.OldItems != null)
{
foreach (var item in e.OldItems.OfType <TSource>())
{
handleOldItem(item);
}
}
if (e.NewItems != null)
{
foreach (var item in e.NewItems.OfType <TSource>())
{
handleNewItem(item);
}
}
break;
case NotifyCollectionChangedAction.Reset:
handleDispose();
if (e.NewItems != null)
{
foreach (var item in e.NewItems.OfType <TSource>())
{
handleNewItem(item);
}
}
break;
}
});
return(Disposable.Create(() =>
{
handleDispose();
collectionObservation.Dispose();
}));
}
