VirtualDataWindow

A loaded page of a larger collection, for data that arrives a page at a time.

The list is sized by totalCount while only items are in memory. Indices are indices in the whole collection: the item at index is items[index - startIndex], and indices the page does not cover render nothing.

Measured sizes are kept per index across pages while totalCount holds: the indices still mean the same records. A page with another totalCount is a different collection, and every size is measured again. A page that keeps the count but puts different records at the same indices keeps the sizes measured for the previous ones until those rows render.