一个 bug / Masonry的引入
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 '$x0 == 0x174c38500'
Breakpoint 113: where = QuartzCore`-[CALayer setBounds:], address = 0x000000018a3eb93c
<GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (160 217.375; 55 6); autoresize = W; layer = <CALayer: 0x174c38500>>
(lldb) break set -F '-[CALayer setBounds:]' -c '$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
看一下赋值过程：
(lldb) po $x0
<CALayer:0x174c38500; position = CGPoint (215 220.375); bounds = CGRect (0 0; 55 6); delegate = <GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (187.5 217.375; 55 6); autoresize = W; layer = <CALayer: 0x174c38500>>; sublayers = (<CALayer: 0x170a3fd40>, <CALayer: 0x1704250a0>, <CALayer: 0x174c38200>, <CALayer: 0x174c38080>); opaque = YES; allowsGroupOpacity = YES; >
<CALayer:0x174c38500; position = CGPoint (215 220.375); bounds = CGRect (0 0; 55 6); delegate = <GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (187.5 217.375; 55 6); autoresize = W; layer = <CALayer: 0x174c38500>>; sublayers = (<CALayer: 0x170a3fd40>, <CALayer: 0x1704250a0>, <CALayer: 0x174c38200>, <CALayer: 0x174c38080>); opaque = YES; allowsGroupOpacity = YES; >
(lldb) finish
(lldb) po 0x174c38500
<CALayer:0x174c38500; position = CGPoint (215 220.375); bounds = CGRect (0 0; 110 6); delegate = <GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (160 217.375; 110 6); autoresize = W; layer = <CALayer: 0x174c38500>>; sublayers = (<CALayer: 0x170a3fd40>, <CALayer: 0x1704250a0>, <CALayer: 0x174c38200>, <CALayer: 0x174c38080>); opaque = YES; allowsGroupOpacity = YES; >
这里借了台iPhone 6/iOS8， cpu是ARM64 所以得参考下面link里bcattle的补充回答，寄存器是$x0, iphone 5/iOS7 上用$r0 但是居然值没变化。模拟器上没成功。另外同样是layoutSubviews 前者是UITableView的，后者是UITableViewCell调用的。
好奇满足了，然后想办法解决。so上搜索PageControl UITableViewCell layoutSubViews／center 等等，没有看到相关讨论。某天学了一点AutoLayout赶紧过来写一行：
1 [pc setTranslatesAutoresizingMaskIntoConstraints:NO]; 2 [cell.contentView addConstraints:[NSLayoutConstraint 3 constraintsWithVisualFormat:@"H:|-0-[pc]-0-|” 4 options:0 5 metrics:nil 6 views:NSDictionaryOfVariableBindings(pc)]]; 7 8 [cell.contentView addConstraints:[NSLayoutConstraint 9 constraintsWithVisualFormat:[NSString stringWithFormat: @"V:|-%f-[pc]-11-|", CGRectGetHeight(scroll.frame)-11-6] 10 options:0 11 metrics:nil 12 views:NSDictionaryOfVariableBindings(pc)]];
不卖关子，成功了。于是结论出来了，AutoLayout升级为必修。Masonry，我来了。
1 [pc mas_makeConstraints:^(MASConstraintMaker * make){ 2 make.bottom.equalTo(cell.contentView.mas_bottom).with.offset(-6); 3 make.centerX.equalTo(cell.contentView.mas_centerX); 4 }];
尾声：storyboard的预览功能＋sizeClass会不会比传统的手码代码快一点呢?
2015.03.30
