autolayout Debug

最新推荐文章于 2018-01-24 18:10:59 发布

转载最新推荐文章于 2018-01-24 18:10:59 发布 · 356 阅读

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对于 iOS 和 OS X 开发者来说，Autolayout已经逐渐变成一个至关重要的开发工具。它让多屏幕适配变得小菜一碟(peasy)，但是有些时候它还是会把我们搞疯掉，因为它总是会出现那些啰嗦又没啥用处的错误警告。

就像这样:

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.
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints)

(...........)  


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.

这么长的错误日志！！！！尼玛让谁看！！！

但是我们仔细看一下，观察 NSLayoutConstraint 部分。发现它倒数第二行还是有给我们点希望去解决这个错误的。在 UIViewAlertForUnsatisfiableConstraints 添加一个Symbolic breakpoint 断点。
既然这样，我们就去试一下…

尼玛！！毛用都没有啊！！它停在了线程堆栈上，然而LLDB依旧一片黑暗…

于是这里就有一个小技巧(Trick)，来让你的symbolic breakpoint变得更加有用。为你的ObjC项目添加
po [[UIWindow keyWindow] _autolayoutTrace]

或者为你的Swift项目添加

expr -l objc++ -O – [[UIWindow keyWindow] _autolayoutTrace]

现在你就会在命令控制台看到你的UIView 的层次结构还有出现错误的地方。

UIWindow:0x7f9481c93360
|   •UIView:0x7f9481c9d680
|   |   *UIView:0x7f9481c9d990- AMBIGUOUS LAYOUT for UIView:0x7f9481c9d990.minX{id: 13}, UIView:0x7f9481c9d990.minY{id: 16}
|   |   *_UILayoutGuide:0x7f9481c9e160- AMBIGUOUS LAYOUT for _UILayoutGuide:0x7f9481c9e160.minY{id: 17}
|   |   *_UILayoutGuide:0x7f9481c9ebb0- AMBIGUOUS LAYOUT for _UILayoutGuide:0x7f9481c9ebb0.minY{id: 27}