ios - 如何在可重用的 UITableViewCell 中设置约束

Question

我的 xib layout likes under drawing除了“c”的高度常量之外，我还设置了从“a”到“b”到...“e”的约束，以便可以确定单元格的高度。有时“c”会隐藏，因为某些原因，当标签可见时，我将高度常量更改为零和实际高度。

--------------------------------------
UILabel(name-singleline)         a
UILabel(title-Multi line)         b
UIView(hidden or not)             c (default height constant = 80)
 -UILabel(content Multi line)     d
UILabel(singleline)               e
--------------------------------------

但是有个autolayout警告让我抓狂

(
    "<NSLayoutConstraint:0x15756760 V:[UILabel:0x15756650'XXXX'(15)]>",
    "<NSLayoutConstraint:0x15757130 V:[UIView:0x15756ee0(80)]>",
    "<NSLayoutConstraint:0x15758060 V:|-(21)-[UILabel:0x15756650'XXXX']   (Names: '|':UITableViewCellContentView:0x157563a0 )>",
    "<NSLayoutConstraint:0x15758120 V:[UILabel:0x15756650'XXXX']-(14)-[Project.GWWLabel:0x157573d0'YYYY']>",
    "<NSLayoutConstraint:0x157581e0 V:[Project.GWWLabel:0x157573d0'YYYY']-(3)-[UIView:0x15756ee0]>",
    "<NSLayoutConstraint:0x15758210 V:[UIView:0x15756ee0]-(8)-[UILabel:0x157569e0'ZZZZ']>",
    "<NSLayoutConstraint:0x15758270 V:[UILabel:0x157569e0'ZZZZ']-(18)-|   (Names: '|':UITableViewCellContentView:0x157563a0 )>",
    "<NSLayoutConstraint:0x1575d760 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x157563a0(139.5)]>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x15757130 V:[UIView:0x15756ee0(80)]>

我也很想知道为什么会这样

Answer 1

试试这个:

将height constraint的priority设置为750如下图当你改变高度常数时它会起作用