支持iOS 6/6 Plus的时候碰到这样一个问题：
　　塞在UITableViewCell里的UIPageControl居中设置失败了，偏右
　　刚刚设置时下断点查看(6Plus模拟器)：
　　<GrayPageControl: 0x7f96a535c350; baseClass = UIPageControl; frame = (179.5 241.75; 55 6); autoresize = W; layer = <CALayer: 0x7f96a535c4a0>>
　　运行后：
　　<GrayPageControl: 0x7f96a535c350; baseClass = UIPageControl; frame = (179.333 241.75; 149 6); autoresize = W; layer = <CALayer: 0x7f96a535c4a0>>
　　好奇在什么时候被改变的，考虑搞个内存修改断点，上lldb，听从忠告检测CALayer的frame改动而不是UIView的：
　　(lldb) po pc
　　<GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (160 217.375; 55 6); autoresize = W; layer = <CALayer: 0x174c38500>>
　　(lldb) break set -F '-[CALayer setBounds:]' -c '$x0 == 0x174c38500'
　　Breakpoint 113: where = QuartzCore`-[CALayer setBounds:]， address = 0x000000018a3eb93c
　　结果是 layoutSubviews:
#0 0x000000018a3eb93c in -[CALayer setBounds:] ()
#1 0x000000018a3ec684 in -[CALayer setFrame:] ()
#2 0x000000018aa9da3c in -[UIView(Geometry) setFrame:] ()
#3 0x000000018aaba7b4 in -[UIView(Geometry) _applyAutoresizingMaskWithOldSuperviewSize:] ()
#4 0x000000018618cfc8 in __53-[__NSArrayM enumerateObjectsWithOptions:usingBlock:]_block_invoke ()
#5 0x000000018618ce6c in -[__NSArrayM enumerateObjectsWithOptions:usingBlock:] ()
#6 0x000000018aaa9f58 in -[UIView(Geometry) resizeSubviewsWithOldSize:] ()
#7 0x000000018aa9daf4 in -[UIView(Geometry) setFrame:] ()
#8 0x000000018ab7b9d4 in -[UITableViewCellContentView setFrame:] ()
#9 0x000000018abe442c in __53-[UITableView _configureCellForDisplay:forIndexPath:]_block_invoke ()
#10 0x000000018aab24c8 in +[UIView(Animation) performWithoutAnimation:] ()
#11 0x000000018abe3b0c in -[UITableView _configureCellForDisplay:forIndexPath:] ()
#12 0x000000018ad9b4d8 in -[UITableView _createPreparedCellForGlobalRow:withIndexPath:willDisplay:] ()
#13 0x000000018ad9006c in -[UITableView _updateVisibleCellsNow:isRecursive:] ()
#14 0x000000018ab84c44 in -[UITableView layoutSubviews] ()
#15 0x000000018aaa14a4 in -[UIView(CALayerDelegate) layoutSublayersOfLayer:] ()
#16 0x000000018a3f57a8 in -[CALayer layoutSublayers] ()
#17 0x000000018a3f0378 in CA::Layer::layout_if_needed(CA::Transaction*) ()
#18 0x000000018a3f021c in CA::Layer::layout_and_display_if_needed(CA::Transaction*) ()
#19 0x000000018a3efa14 in CA::Context::commit_transaction(CA::Transaction*) ()
#20 0x000000018a3ef798 in CA::Transaction::commit() ()
#21 0x000000018a3e91c8 in CA::Transaction::observer_callback(__CFRunLoopObserver*， unsigned long， void*) ()
#22 0x000000018624ed98 in __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ ()
#23 0x000000018624bd24 in __CFRunLoopDoObservers ()
#24 0x000000018624c104 in __CFRunLoopRun ()
#25 0x00000001861791f4 in CFRunLoopRunSpecific ()
#26 0x000000018f59b6fc in GSEventRunModal ()
#27 0x000000018ab0a10c in UIApplicationMain ()
#28 0x0000000100029ce0 in main