ios - CPU usage dropping as UIScrollView gets larger? -


experiencing strange phenomenon. app built around vertical uiscrollview (i.e. "the feed") activity timeline facebook's. when user scrolls bottom, feed can load older items in blocks of 20.

the first 0-20 items (default load) scroll fast , continues scroll fast when items 20-40 added, performance degrades when items 40-60 added , app becomes unusable when 60-80 added.

what's extremely odd cpu usage during entire scenario:

  • 20 feed items (default): cpu 65%
  • 40 feed items: cpu 40%, thread 1 activity down 25% (eyeballing)
  • 60 feed items: cpu 18%, thread 1 down 50% previous
  • 80 feed items: cpu 7%, thread 1 down 50% previous again

this leading me believe lack of performance not size of scroll view else causing cpu disengage in strange way. you'd expect cpu utilization increase, not decrease.

i thought perhaps inadvertently adding new feed items not on main thread , somehow screwing up, that's not case.

any thoughts?

fyi (iphone 5 running ios8, app built ios 8 sdk, don't think experiencing when building ios 7 sdk running on ios 7. performance degraded, but, iirc, predictably uiscrollview size - attempt confirm).

update built , ran app both 7 sdk , 8 sdk on iphone 4s running ios 7.0.6. not showing same issue. scrollview performance degrades more predictably , cpu usage not drop uiscrollview increases in size. bug in ios 8??

you should consider switching uitableview. designed avoid exact problem. when cells go off view, re-used cells being used. avoids allocating many of them. why contact list, ipod songs, facebook feed, etc don't degrade when table grows bigger.


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