ZIKConstraintsGuard

A tool for debugging iOS view constraint.Monitor constraint conflict and crash problem below iOS7.

Features

• monitor constraint conflict.
• monitor crash below iOS7 causing by layoutSubviews.
• callback with more information:
  • the UIView where conflict happened
  • the view controller
  • all current constraints
  • the constraint to be breaked
  • view hierarchy

With the view and view controller, you can quickly find out the exactly wrong constraint and which view it came from.

Apple's bug below iOS7

When implementation your custom view's layoutSubviews, remember:

• Call [super layoutSubviews].

• Don't add constraints in layoutSubviews.

If not, adding subview to this view in iOS6 or iOS7 will crash you app with 'Auto Layout still required after executing - layoutSubviews..' printed in console.Apple fixed this after iOS8.

Some system view like UITableView,UITableViewCell doesn't call [super layoutSubviews]. So don't add subview to them in iOS6 and iOS7, or you can use method swizzling to fix them.

If your app need to support iOS7,this will offer a great help,since Xcode8 can't debug iOS7 device any more.

CocoaPods

To your podspec add:

pod 'ZIKConstraintsGuard'

How to use

//monitor constraint conflict
[ZIKConstraintsGuard monitorUnsatisfiableConstraintWithHandler:^(UIView *view, 
																 UIViewController *viewController, 
																 NSLayoutConstraint *constraintToBreak, 
																 NSArray<NSLayoutConstraint *> *currentConstraints, 
																 NSString *description) {
        
    NSString *className = NSStringFromClass([viewController class]);
    if ([className hasPrefix:@"UI"] && ![className isEqualToString:@"UINavigationController"]) {
        NSLog(@"ignore conflict in system view:%@",viewController);
        return;
    }
    
    //formatted description with enough debugging info, write to your log file
    NSLog(@"%@",description);
}];

//monitor crash below iOS7
[ZIKConstraintsGuard monitorErrorFromLayoutviewsWithHandler:^(UIView * _Nonnull view, UIViewController * _Nullable viewController, NSString * _Nonnull description) {
        
    //write error info to your log file before crash
    NSLog(@"%@",description);
}];

How it works

Hook private API to get the UIView.Then get other informations from the UIView.

API when meet unsatisfiable constraint:

-[UIView engine:willBreakConstraint:dueToMutuallyExclusiveConstraints:]

API when system checking if view miss to call super layoutSubviews:

-[UIView _wantsWarningForMissingSuperLayoutSubviews]

These private API names were encrypted when using,in case you want to use this tool in an AppStore app.

---

一个调试iOS约束的工具。可以检测约束冲突和iOS7以下的crash问题。

功能

• 监控约束冲突。
• 监控iOS7以下系统UIView中的layoutSubviews导致的crash。
• 发生冲突时，回调附带更多关键信息：
  • 冲突所在的view
  • 冲突所在的view controller
  • 目前所有的约束
  • 系统将要打破的约束
  • view层级

通过捕捉到的view和view controller，就可以快速地找到是哪个界面的哪个控件的哪个约束出现了问题。

自动布局在iOS7以下的bug

当你在实现自定义view的layoutSubviews方法时，记住：

• 调用[super layoutSubviews]
• 不要在layoutSubviews里增加约束

如果不遵守这两条，当你向这个view上增加子view时，在iOS6和iOS7上会crash，控制台会输出提示：'Auto Layout still required after executing - layoutSubviews..' 。iOS8开始则不会crash。

某些系统控件，例如UITableView，UITableViewCell没有调用[super layoutSubviews]，所以在iOS6和iOS7上不能在它们上面增加子view，除非你用method swizlling修复它们的layoutSubviews方法。

当你的app需要支持iOS7时，这个工具会提供很大帮助。因为Xcode8已经不支持iOS7的调试了。

CocoaPods

添加:

pod 'ZIKConstraintsGuard'

使用方法

见英文部分： 使用方法

实现原理

替换了两个私有API，获取对应的view，再从view里获取其他相关信息。

当遇到约束冲突时的API:

-[UIView engine:willBreakConstraint:dueToMutuallyExclusiveConstraints:]

系统用于检测当前view是否调用了[super layoutSubviews]的API:

-[UIView _wantsWarningForMissingSuperLayoutSubviews]

这些私有API名字已经经过混淆。