Hello, I'm having an issue with XamComboEditor whereby occasionally the function

ItemPanelBase.RenderItem<T2, TControl2>(T2 comboEditorItem, Size availableSize) in your code is called with a null comboEditorItem causing a crash;

I've looked a bit into it and it seems like the function MeasureOverride is responsible for passing the null value in;

The null value is passed in via this line in your ItemsPanelBase.RenderOverride function

Size firstItemSize = this.RenderItem(firstItem, availableSize);  //firstItem is null

Looks like this is something to do with the management of the VisibleItems list

I can reproduce this issue by putting a variety of different kinds of items into the combobox and clicking on the drop-down arrow repeatedly until eventually the render function crashes;

Oh, also as a side note you have some truly, truly, awful code which has caused me no ends of headaches in the DataManagerBase.ResolveIndexForRecord function

In this buggy heap of garbage code  if it's bound to a list will use equality comparer and if its bound to something else, like an array or IEnumerable, will scan through it using reference ==

This means that the behavior of your combobox can change radically whether I bind to an IList or an IEnumerable, very not good.

        public int ResolveIndexForRecord(object data)

        {

            if (this._sortedFilterDataSource == null)

            {

                if (this.IListData != null)

                    return this.IListData.IndexOf(data);

                else

                {

                    int index = -1;

                    foreach (object current in this.OriginalDataSource)

                    {

                        index++;

                        if (current == data)

                            return index;

                    }

                }

            }

            else

            {

                return this._sortedFilterDataSource.IndexOf(data);

            }

            return -1;

        }

IndexOf
This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

==

By default uses reference compare

 
These two things are obviously a lot different, you shouldn't be switching between them.