For the project I'm working on we ran into a performance issue on iPhone4 where an interaction would lock up the phone for a few seconds. It ran fine on iPhone5 and in the Simulator, but there was a severe hangup in on the older device. Investigation in Instruments revealed to problem to be autolayout. A lot of time (>3 seconds) was spent recalculating layout.
So I first hunted for
[view layoutIfNeeded] calls, replacing them by
[view setNeedsLayout] where applicable (sometimes you actually want to layout immediately if you need to do more stuff based on the layout results, but this is rarely the case). To no real avail, the issue remained extremely slow.
Digging in further, I found that two different call trees were doing autolayout of a certain part of the screen at the same time. This was all happening on the main thread which explained the lockup (no surprises there though). But in the timespan of the 2 seconds Instruments reported where (the major part of the) lockup was, there were two blocks where setting a label caused at least 800ms of autolayout calculations. So that's 1.6s accounted for. Which seemed like a good starting point to optimize.
The code was just setting properties (in this case: a title label and a response handler block), but they both touched the same label twice. I pondered on coalescing the two properties in one method but it seemed like an unsatisfying solution. And so I decided to copy a pattern Apple uses too regarding UI: the 'setNeedsLayout' pattern.
Brent Simmons touches on the use of abbreviations in Cocoa. I've noticed this behaviour too, and other uncocoalike things too. This is especially apparant in code of devs coming from other programming language/platforms.
So, it's that time of the year again. WWDC is almost upon us. Like last year, I won't be able to make it due to "agenda issues" (mainly the same as last year, but that's what happens when you have kids). But also I'm in the midst of an app release at work and as a team/tech lead it would be less than ideal to skip a week for WWDC (which is actually more than a week since there's the Jetlag Recovery Period too). So it wasn't in the stars this year.
I think I might be going again next year. Not sure if I will go for WWDC itself, but certainly for an AltWWDC experience. There's a lot of people going to SF next week which I'd really like to meet or talk to again. Sure, there's twitter, but nothing beats IRL contact. And the buzz around WWDC is just so invigourating, or at least it was in 2012, IMHO. So we'll see. I'll have some money set aside for next year, so at least that won't be a problem.