Scroll position cache not purged on update

Hi, me and @giuseppeg stumbled over an issue in case of a chat with reverse scrolling behavior + scrollToIndex option. When a raw of a List gets updated and its height becomes bigger, RV is currently not recalculating the scroll position. Value of scrollToIndex remains the same before and after the update.

[bvaughn]

FYI I’ve caught this in a small unit test:

it('should update scroll position to account for changed cell sizes', () => {
  let rowHeight = 20
  const props = {
    height: 100,
    rowCount: 100,
    rowHeight: ({ index }) => index === 99 ? rowHeight : 20,
    scrollToRow: 99
  }
  const grid = render(getMarkup(props))
  const node = findDOMNode(grid)
  expect(node.scrollTop).toBe(1900)
  rowHeight = 40
  grid.recomputeGridSize({
    rowIndex: 99
  })
  expect(node.scrollTop).toBe(1920)
})

The behavior demonstrated is because of this check. The helper doesn’t have enough information to detect when a cell size has changed if the size is determined by a function property.

I think the most appropriate fix is to set a flag when cell sizes are recomputed to tip the next cDU off that its scroll offset may be invalid.

Will be fixed in 9.0.1 (releasing presently)

[bvaughn]

That’s a good workaround 😁 Maybe once I get 9.0.0 shipped and give it a few days for any bug reports to trickle in, I can dig into this more