ObservableCollection : calling OnCollectionChanged with multiple new items

Question

please note that I am trying to use NotifyCollectionChangedAction.Add action instead of .Reset. the latter does work, but it is not very efficient with large collections.

so i subclassed ObservableCollection:

public class SuspendableObservableCollection<T> : ObservableCollection<T>

for some reason, this code:

private List<T> _cachedItems;
...

    public void FlushCache() {
        if (_cachedItems.Count > 0) {

        foreach (var item in _cachedItems)
            Items.Add(item);

        OnCollectionChanged(new NotifyCollectionChangedEventArgs(
            NotifyCollectionChangedAction.Add, (IList<T>)_cachedItems));
        }
    }

is throwing A collection Add event refers to item that does not belong to collection

this appears to be a bug in BCL ?

I can step through and see prior to calling OnCollectionChanged that new items are added to this.Items

WOW

just made a staggering discovery. None of these approaches worked for me (flush, addrange), because the error appears to be triggered ONLY if this collection is bound to my Listview!!

TestObservableCollection<Trade> testCollection = new TestObservableCollection<Trade>();
List<Trade> testTrades = new List<Trade>();

for (int i = 0; i < 200000; i++) 
    testTrades.Add(t);

testCollection.AddRange(testTrades); // no problems here.. 
_trades.AddRange(testTrades); // this one is bound to ListView .. BOOOM!!!

In conclusion, ObservableCollection does support adding incremental lists, but a ListView doesn't. Andyp figured out a workaround to make it work with CollectionView below, but since .Refresh() is called, that is no different than just calling OnCollectionChanged( .Reset )..

Answer 1

I believe you need to cast it to an IList:

base.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, (IList)_cachedItems));

Answer 2

Hi,

you can implement AddRange() for the ObservableCollection like this as shown here:

public class RangeObservableCollection<T> : ObservableCollection<T>
{
    private bool _SuppressNotification;

    public override event NotifyCollectionChangedEventHandler CollectionChanged;

    protected virtual void OnCollectionChangedMultiItem(
        NotifyCollectionChangedEventArgs e)
    {
        NotifyCollectionChangedEventHandler handlers = this.CollectionChanged;
        if (handlers != null)
        {
            foreach (NotifyCollectionChangedEventHandler handler in 
                handlers.GetInvocationList())
            {
                if (handler.Target is CollectionView)
                    ((CollectionView)handler.Target).Refresh();
                else
                    handler(this, e);
            }
        }
    }

    protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
    {
        if (!_SuppressNotification)
        {
            base.OnCollectionChanged(e);
            if (CollectionChanged != null)
                CollectionChanged.Invoke(this, e);
        }
    }

    public void AddRange(IEnumerable<T> list)
    {
        if (list == null)
            throw new ArgumentNullException("list");

        _SuppressNotification = true;

        foreach (T item in list)
        {
            Add(item);
        }
        _SuppressNotification = false;

        OnCollectionChangedMultiItem(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add, list));
    }
}

UPDATE: After binding to ListBox I was seeing an InvalidOperationException too (same message you were seeing). According to this article that's because CollectionView doesn't support range actions. Luckily the article also supplies a solution (although it feels a little "hack-ish").

UPDATE 2: Added a fix that raises the overridden CollectionChanged event in the overridden implementation of OnCollectionChanged().