/// <summary>
/// Creates a collection whose contents will "follow" another
/// collection; this method is useful for creating ViewModel collections
/// that are automatically updated when the respective Model collection
/// is updated.
/// </summary>
/// <param name="selector">A Select function that will be run on each
/// item.</param>
/// <returns>A new collection whose items are equivalent to
/// Collection.Select(selector) and will mirror the initial collection.</returns>
public static ReactiveCollection <TNew> CreateDerivedCollection <T, TNew>(
this ObservableCollection <T> This,
Func <T, TNew> selector)
{
Contract.Requires(selector != null);
#if !IOS // Contract.Result is borked in Mono
Contract.Ensures(Contract.Result <ReactiveCollection <TNew> >().Count == This.Count);
#endif
var ret = new ReactiveCollection <TNew>(This.Select(selector));
var coll_changed = new Subject <NotifyCollectionChangedEventArgs>();
This.CollectionChanged += (o, e) => coll_changed.OnNext(e);
/* XXX: Ditto as from above
* var coll_changed = Observable.FromEvent<NotifyCollectionChangedEventHandler, NotifyCollectionChangedEventArgs>(
* x => This.CollectionChanged += x, x => This.CollectionChanged -= x);
*/
coll_changed.Subscribe(x => {
switch (x.Action)
{
case NotifyCollectionChangedAction.Add:
case NotifyCollectionChangedAction.Remove:
case NotifyCollectionChangedAction.Replace:
// NB: SL4 fills in OldStartingIndex with -1 on Replace :-/
int old_index = (x.Action == NotifyCollectionChangedAction.Replace ?
x.NewStartingIndex : x.OldStartingIndex);
if (x.OldItems != null)
{
foreach (object _ in x.OldItems)
{
ret.RemoveAt(old_index);
}
}
if (x.NewItems != null)
{
foreach (T item in x.NewItems.Cast <T>())
{
ret.Insert(x.NewStartingIndex, selector(item));
}
}
break;
case NotifyCollectionChangedAction.Reset:
ret.Clear();
break;
default:
break;
}
});
return(ret);
}