private static void HandleCollectionChanged <T>(IList <T> list,
IListMonitor <T> monitor, NotifyCollectionChangedEventArgs e)
{
int position = 0;
switch (e.Action)
{
case NotifyCollectionChangedAction.Add:
position = e.NewStartingIndex;
foreach (var item in e.NewItems?.Cast <T>() ?? Array.Empty <T>())
{
monitor.NewItem(item, position++);
}
break;
case NotifyCollectionChangedAction.Remove:
position = e.OldStartingIndex;
foreach (var item in e.OldItems?.Cast <T>() ?? Array.Empty <T>())
{
monitor.DestroyItem(item, position++);
}
break;
case NotifyCollectionChangedAction.Replace:
if (e.NewItems == null || e.OldItems == null)
{
break;
}
for (int i = 0; i < e.NewItems.Count; i++)
{
if (e.OldItems[i] is T oldItem)
{
monitor.DestroyItem(oldItem, e.OldStartingIndex + i);
}
if (e.NewItems[i] is T newItem)
{
monitor.NewItem(newItem, e.NewStartingIndex + i);
}
}
break;
case NotifyCollectionChangedAction.Move:
monitor.Move(e.OldStartingIndex, e.NewStartingIndex, e.NewItems?.Count ?? 0);
break;
case NotifyCollectionChangedAction.Reset:
monitor.Reset();
if (e.OldItems != null)
{
Clearing(e.OldItems.OfType <T>(), monitor);
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
private static void Clearing <T>(IEnumerable <T> list, IListMonitor <T> monitor)
{
int position = 0;
foreach (var item in list)
{
monitor.DestroyItem(item, position++);
}
}
public static Action AttachToList <T, TList>(this IListMonitor <T> monitor, TList list) where TList :
ObservableCollectionWithProperClearMethod <T>, INotifyCollectionChanged
{
void CollectionChanged(object s, NotifyCollectionChangedEventArgs e) => HandleCollectionChanged(list, monitor, e);
list.CollectionChanged += CollectionChanged;
monitor.Initalize(list);
return(() => list.CollectionChanged -= CollectionChanged);
}
