看一下赋值过程：
　　(lldb) po $x0
　　<CALayer:0x174c38500; position = CGPoint (215 220.375); bounds = CGRect (0 0; 55 6); delegate = <GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (187.5 217.375; 55 6); autoresize = W; layer = <CALayer: 0x174c38500>>; sublayers = (<CALayer: 0x170a3fd40>， <CALayer: 0x1704250a0>， <CALayer: 0x174c38200>， <CALayer: 0x174c38080>); opaque = YES; allowsGroupOpacity = YES; >
　　(lldb) finish
　　(lldb) po 0x174c38500
　　<CALayer:0x174c38500; position = CGPoint (215 220.375); bounds = CGRect (0 0; 110 6); delegate = <GrayPageControl: 0x15fe26ca0; baseClass = UIPageControl; frame = (160 217.375; 110 6); autoresize = W; layer = <CALayer: 0x174c38500>>; sublayers = (<CALayer: 0x170a3fd40>， <CALayer: 0x1704250a0>， <CALayer: 0x174c38200>， <CALayer: 0x174c38080>); opaque = YES; allowsGroupOpacity = YES; >
　　这里借了台iPhone 6/iOS8， cpu是ARM64 所以得参考下面link里bcattle的补充回答，寄存器是$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。
　　http://stackoverflow.com/questions/13976219/how-do-i-set-an-lldb-watchpoint-on-a-property-of-self-view
　　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?