UITableView scrolls weirdly on reloadRows

Originator:futuretap
Number:rdar://46806232 Date Originated:18-Dec-2018 11:44 AM
Status:Open Resolved:
Product:iOS + SDK Product Version:12.1.2 (16D5024a)
Classification:UI/Usability Reproducible:Always
 
Summary:
A UITableView with a large tableHeaderView shortly scrolls to a wrong contentOffset and back when reloading a row in a begin/endUpdates block.

Steps to Reproduce:
Build and run the attached sample project.
Using the + button, add that many rows to the table that when scrolled all the way to the bottom, a small part of the tableHeaderView is still visible. (On an iPhone XS, 11 cells is a good number.)
Scroll all the way to the bottom so that only a small part of the tableHeaderView is still visible.
Now tap on the first cell to select it. This causes a reload of the cell in a begin/endUpdates block.

Expected Results:
The cell content should be reloaded but there should be no scrolling.

Actual Results:
It scrolls from a start contentOffset of {0, 287} to {0, 144} and {0, 105}, then back to {0, 287}. (I obtained the offset values by setting a breakpoint in `-[UITableView setContentOffset:]`.)

Version:
12.1.2 (16D5024a)

Notes:
Included in the project, I've attached a screen video to show the issue.

When removing the tableHeaderView, the issue does not occur anymore.

Comments

Addendum 2

When disabling estimatedRowHeight and calculating rowHeight manually the issue does not occur anymore. So the bug seems to be involving row height estimation. https://github.com/futuretap/r46806232/tree/manualCellHeight

By futuretap at Dec. 18, 2018, 12:17 p.m. (reply...)

Addendum

I tried to replace the tableHeaderView with a large first cell of the same height. The issue also occurs. See https://github.com/futuretap/r46806232/tree/largeFirstCell

By futuretap at Dec. 18, 2018, 11 a.m. (reply...)

Sample project: https://github.com/futuretap/r46806232

By futuretap at Dec. 18, 2018, 10:48 a.m. (reply...)

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