iOS scroll bounce fix - skip event if scrollTop < 0

[toddtarsi]

If we're at a scrollTop above 0, just avoid triggering the scroll event entirely, or maybe I should pass the event through.
This is a McDonalds fix, feel free to critique this as needed. Thanks!
Resolves #532

[bvaughn]

Hey @toddtarsi,

This fix seems reasonably safe- but I'd really like to be able to reproduce the problem and verify that this change fixes it before merging.

Any chance I could get a more detailed description of how to reproduce the behavior? Or a video demo?

[bvaughn]

PS. Thanks for the PR 😁

[toddtarsi]

Absolutely, I am filming local iOS device repro using the demo server. :)
Will have shortly.

[toddtarsi]

Okay, I had some issues with the demo server, so I ended up using my team's application to demonstrate the fix:

PFA using the standard virtualized list (technically infinite loader, but irrelevant here when everything is loaded):

PFA using the virtualized list after this fix:

[bvaughn]

Thanks! This is great. Very helpful.

[maxsalven]

Hi @bvaughn @toddtarsi,

This fix solved issues when scrolling upwards, however I still get visual flickers when over scrolling downwards past the bottom of a list.

Let me know if you are unable to reproduce, I can try capture a video somehow if so. Many thanks.

[toddtarsi]

@maxsalven -

Nah. That issue makes sense. In the same way this avoids recalculating the render when scrolling above the beginning, I figured at some point we'd need to resolve this issue when scrolling past the end as well. If you could help me out by demoing if the fix (#616) resolves your issue, I would be appreciative.

@bvaughn - Sorry I didn't include this in the original fix, but I wrote a small patch for it here: #616