RFR: 8320232: Cells duplicated when table collapsed and expanded

[Marius Hanl]

On Mon, 29 Jul 2024 18:45:23 GMT, Marius Hanl <mhanl at openjdk.org> wrote:

> This PR fixes a bug where a `TableView` inside a `TitledPane` may 'duplicate' the cells. This actually has nothing to do with the `TitledPane`, but it triggered the bug easily due to its nature to change the size of his content when collapsing.
> 
> The expansion change of a `TitledPane` triggered an event where the underlying `VirtualFlow` was adding cells to the pile (for reuse) and later cleaning them all up without resetting the index to -1. 
> This led to a bug where two cells had the same index and therefore received an edit event, although just one should (and is visible, the other cell has no parent -> orphan node).
> 
> The fix is to always reset the index to -1. This was already done before, just not everywhere, for all cells.
> So before we clear the pile (or cells), we always reset the index to -1.
> Added a bunch of tests, some pass before and after.

I agree the minor change is unrelated, but since it is that small for a test I had written in the past, I decided to keep it.

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PR Comment: https://git.openjdk.org/jfx/pull/1521#issuecomment-2266718230