In UIViewLazyList's UITableView, adding special-case handling for programmatic scroll-to-top calls

[dnagler]

• CHANGELOG.md's "Unreleased" section has been updated, if applicable.

[dnagler]

I know that this method should not be called for programmatic scrolls, but without this call, the placeholders at the top of the scrollView remain in place after the scroll animation finishes, without being swapped out for rendered widgets.

With this call in place, we see two animations: the scroll itself (up to the top of the scrollView), followed by a second animation where the "wall of placeholders" being shown collapses upward, to be replaced with rendered widgets.

Is there a better hook to call here? Ideally the placeholders would swap out for rendered widgets without the second animation after the scroll finishes.

[dnagler]

cc @swankjesse

[dnagler]

I played around with some alternatives, replacing the scrollViewDidScroll(scrollView) call with each of the following:

• updateProcessor.onEndChanges()
• (scrollView as? UITableView)?.reloadData()
• scrollView.setNeedsDisplay()

but all of them kept the "wall of placeholders" in place. I wish we could do something akin to the lazyPagingItems.refresh() call we're doing in the Treehouse layer, which repopulates the feed without animation.

[dnagler]

Marginal improvement: rather than keeping track of wasDoingProgrammaticScroll, it's better to just use the native scrollViewDidScrollToTop hook (which is actually fired earlier than this hook).

This feels better, but the above concern (needing to get rid of the second animation) remains to be addressed.

[JakeWharton]

Would prefer Jesse take a look still

[underscoretang]

Just to confirm before merging. Did you test this on the money app from regressions?

[dnagler]

Just to confirm before merging. Did you test this on the money app from regressions?

I'm not seeing anything happen at all when tapping on the tab bar icon for the Money tab--looks like scroll-to-top behavior hasn't been implemented on the client side yet?

[underscoretang]

Oh yeah, the tab button isn't hooked up (not sure if that's part of the plan, but does tapping to status bar still work?

It will scroll to top for us rn without doing anything extra

[dnagler]

Oh yeah, the tab button isn't hooked up (not sure if that's part of the plan, but does tapping to status bar still work?

It will scroll to top for us rn without doing anything extra

Yep, that still works as expected!

[dnagler]

Would prefer Jesse take a look still

Chatted offline with Jesse--will pair with him on this tomorrow, but this change is good to land as-is, as an incremental improvement.