About the scrolling behavior of the List component

The List class uses a fairly complex algorithm for scrolling. A list only lays out as many rows as it can display at once; items beyond the value of the rowCount property don't get rows at all. When the list scrolls, it moves all the rows up or down (depending on the scrolling direction). The list then recycles the rows that are scrolled out of view; it reinitializes them and uses them for the new rows being scrolled into view. To do this, it sets the value of the old row to the new item in the view and moves the old row to where the new item is scrolled into view.

Because of this scrolling behavior, you cannot expect a cell to be used for only one value. Recycling of rows means that the cell renderer must know how to completely reset its state when it is set to a new value. For example, if your cell renderer creates an icon to display one item, it might need to remove that icon when another item is rendered with it. Assume your cell renderer is a container that will be filled with numerous item values over time, and it has to know how to completely change itself from displaying one value to displaying another. In fact, your cell should even know how to properly render undefined items, which might mean removing all old content in the cell.

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