前言
在做项目的时候，无意间看到自动布局约束警告，开始也也觉得没什么，虽然有警告，但并不影响UI展示效果。但是越来越有代码洁癖的我，也忍受不了控制台输出一大堆约束警告Log，于是就查阅如何定位解决约束冲突，同时自己也记录下来。下面开始介绍具体操作步骤吧。
一、添加UIViewAlertForUnsatisfiableConstraints断点
- 添加Symbolic Breakpoints
屏幕快照 2018-06-04 下午2.44.35.png - 编辑断点symbol填入
UIViewAlertForUnsatisfiableConstraints
- 添加控制台打印action
po [[UIWindow keyWindow] _autolayoutTrace]
屏幕快照 2018-06-04 下午2.44.50.png
二、定位约束警告冲突
- 添加好断点之后，当界面有约束冲突，就会触发断点，控制打印如下：
[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.
(
<MASLayoutConstraint:0x604000ab04a0 UIButton:0x7faf99f04010.width == 40>,
<MASLayoutConstraint:0x604000ab66e0 UIButton:0x7faf99f04010.left == CYBButtonView:0x7faf99f83360.left + 10>,
<MASLayoutConstraint:0x604000abaa00 UILabel:0x7faf99f5f8e0.left == UIButton:0x7faf99f04010.right>,
<MASLayoutConstraint:0x604000abd580 UILabel:0x7faf99f5f8e0.left == CYBButtonView:0x7faf99f83360.left + 15>,
)
Will attempt to recover by breaking constraint
<MASLayoutConstraint:0x604000ab04a0 UIButton:0x7faf99f04010.width == 40>
Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
- 根据提示，找到约束有问题的控件地址0x7faf99f04010，然后全局搜索，就能找到具体是哪个控件
- 如果控制台打印不够直观看出是哪个控件约束有问题，我们可以通过 LLDB命令工具chisel定位寻找。
三、解决冲突
通常解决冲突的方法有：
- 删除多余约束
- 修改约束优先级
