变更记录

序号	录入时间	录入人	备注
1	2016-01-05	Alfred Jiang	-

方案名称

Auto Layout - 约束冲突断点调试方法

关键字

Auto Layout \ 调试 \ 断点 \ 约束冲突

需求场景

遇到 Auto Layout 约束冲突时

参考链接

NSHint - Autolayout Breakpoints

详细内容

当遇到以下 Auto Layout 约束冲突提示时

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.

可以通过添加以下断点定位约束冲突

通过添加以下设置，可以观察到全部的 UIView 层级关系以及 AMBIGUOUS LAYOUT 提示（AMBIGUOUS LAYOUT 即为约束冲突或不完善位置），更好的定位约束冲突

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}

还可以通过 expr 命令动态修改页面参数，帮助定位控件位置

(lldb) expr ((UIView *)0x7f9ea3d43410).backgroundColor = [UIColor redColor]
(UICachedDeviceRGBColor *) $1 = 0x00007f9ea3d43410