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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
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  • 添加控制台打印action
po [[UIWindow keyWindow] _autolayoutTrace]
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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.
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  • 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?

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