iOS不同系统的区别，注意点

总结一下开发过程遇到的特殊情况，需要注意的点

iOS9-iOS11的系统使用Xib布局cell，设置UITableViewAutomaticDimension自动计算高度时会提示如下的错误。解决办法，可以给其中一个高度约束设置priority小于1000。iOS12的系统不会出现此错误提示。

2019-08-22 13:29:16.973702+0800 BoChuang[58487:1511846] [LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "",
    "",
    "",
    "",
    "",
    ""
)

Will attempt to recover by breaking constraint 


Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in  may also be helpful.