iOS定位处理约束冲突

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

参考

1、How to trap on UIViewAlertForUnsatisfiableConstraints?