在调试过程中有时候需要查看一个view上的所有子视图，通过lldb命令能够快速查看，
命令如下：
<code>po [headView recursiveDescription]</code>
这里的headView就是需要查看子视图的view
打印的结果如下：
<code>
(lldb) po [headView recursiveDescription]
<ReusableView: 0x1013764b0; baseClass = UICollectionReusableView; frame = (0 560; 375 45); hidden = YES; layer = <CALayer: 0x17422f760>>
| <UIButton: 0x101376690; frame = (0 0; 375 45); opaque = NO; layer = <CALayer: 0x17422f440>>
| | <UIImageView: 0x101376b30; frame = (0 0; 375 45); clipsToBounds = YES; opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x17422f680>>
| | <UIImageView: 0x101376950; frame = (10 17; 7 11); opaque = NO; userInteractionEnabled = NO; layer = <CALayer: 0x17422f560>>
| | <UIButtonLabel: 0x1012dabb0; frame = (27 12; 30.5 21.5); text = 'title'; opaque = NO; userInteractionEnabled = NO; layer = <_UILabelLayer: 0x170292200>>
| <UILabel: 0x101376d10; frame = (305 0; 60 45); userInteractionEnabled = NO; layer = <_UILabelLayer: 0x174284510>>
| | <_UILabelContentLayer: 0x17042a3a0> (layer)
</code>
能够看到子视图的frame 交互性等。