DataGrid row request patterns with data virtualization

I implemented a data virtualization solution using some ideas from CodePlex and the blog of Bea Stollnitz and Vincent Da Ven Berhge's paper (same link). However I needed a different approach so I decided to write my own solution.

I am using a DataGrid to display about a million rows with this solution. I am using UI virtualization as well. My solution is feasible, but I experience some weird behavior in certain situations on how the DataGrid requests data from its source.

About the solution

I ended up writing a list which does all the heavy work. It is a generic class named VirtualList<T>. It implements the ICollectionViewFactory interface, so the collection view creation mechanism can create a VirtualListCollectionView<T> instance to wrap it. This class inherits from ListCollectionView. I did not follow the suggestions to write my own ICollectionView implementation. Inheriting seems to work fine as well.

The VirtualList<T> splits the whole data into pages. It gets the total item count and every time the DataGrid requests for a row via the list indexer it loads the appropriate page or returns it from the cache. The pages are recycled inside and a DispatcherTimer disposes unused pages in idle time.

Data request patterns

• The first thing I learned, that VirtualList<T> should implement IList (non generic). Otherwise the ItemsControl will treat it as an IEnumerable and query/enumerate all the rows. This is logical, since the DataGrid is not type safe, so it cannot use the IList<T> int