Fix typing performance by avoiding expensive UI operations #5913
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Anderas
requested review from
a team,
ismailgulek and
gileluard
and removed request for
a team and
ismailgulek
gileluard
suggested changes
Mar 24, 2022
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| - (void)viewDidLayoutSubviews | ||
| { | ||
| [super viewDidLayoutSubviews]; | ||
| BOOL didViewChangeFrame = !CGRectEqualToRect(lastViewFrame, self.view.frame); | ||
| lastViewFrame = self.view.frame; |
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I do agree that viewDidLayoutSubviews can be called for many reasons and very often indeed. Storing the last view frame is fine but I usually store the last bounds of the view as we're interested by the dimension of the view more than its position.
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Yea thats valid, changed.
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Relates to #5906
Root cause
There are a few things going on here, and all related to an insane amount of spaghetti layout code in RoomViewController. Often time a simple sounding method will internally call other less innocent code, escalating the performance cost This is what I observed:
viewDidLayoutSubviewwe will try to scroll back to the bottom, even if the size of the view has not really changed. The scrolling itself would be fine, but it is one of those methods that trigger a number of other heavy updates (e.g.updateViewControllerAppearanceOnRoomDataSourceState). Note thatviewDidLayoutSubviewis called every time you type a character, which means that when typing fast we are essentially doing all of this expensive work many times per second.refreshRoomTitlemore often (I eat my words about no performance impact) has made this even worse, becauserefreshRoomTitleis one of those very long methods with ton of side effects that are not easy to see. This is I believe also why we started seeing this issue worse in the latest release.Solution
The solution to this is patchwork, because the code is too messy for a simple fix:
MXFileStoreafter typing every single characted (see Do not commit to file store after typing a single character matrix-org/matrix-ios-sdk#1422)Before my changes typing rapidly would consume around 33% of CPU on iPhone 13 Pro. After the changes it dropped to around 17%. We can certainly do more to bring this down.
I am not able to confirm yet whether this also solves the battery drain issue, but using CPU must be at least partly responsible for it.