A debugging tool that catches unsatisfiable constraint errors as they appear at the console and provides call backs either directly to blocks or via NSNotificationCenter. This allows such errors to be handled at runtime.

This tool is intended for debugging only, and has not been designed for production-level performance.

• Highlighting constraint issues during development visually
• Catching constraint problems during unit testing
• Failing UI tests by killing the application on receipt of a constraint error.

To run the example project, clone the repo, and run pod install from the Example directory first.

The example project shows a use of the detector to highlight UIViews with unsatisfiable constraints, displaying a red border on problem views.

YXTUnsatisfiableConstraintsDetector supports projects for iOS 7 and above.

To install manually, copy the files under Pod/Classes into your project.

YXTUnsatisfiableConstraintsDetector is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod "YXTUnsatisfiableConstraintsDetector"

To import the detector into a given source file:

#import "YXTUnsatisfiableConstraintsDetector.h"

You can then instantiate an instance of YXTUnsatisfiableConstraintsDetector and add callback blocks using the registerBlock: method. When all your blocks are configured, call beginMonitoring to start listening for errors.

It is recommended to create a single instance of YXTUnsatisfiableConstraintsDetector in your AppDelegate's launch method, and to enclose this in a DEBUG check to ensure it is not called in release builds. For example, to register a callback that marks views with errors in red:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
#ifdef DEBUG
    YXTUnsatisfiableConstraintsDetector *detector = [[YXTUnsatisfiableConstraintsDetector alloc] init];
    [detector registerBlock:^(UIView *view){
        if(view != nil){
            dispatch_async(dispatch_get_main_queue(), ^(void){
                view.layer.borderColor = [UIColor redColor].CGColor;
                view.layer.borderWidth = 3.0;
            });
        }
    }];
    [detector beginMonitoring];
#endif
    return YES;
}

Note that view may be null if the problem UIView is not currently in the view hierarchy.

Tom Elliott, [email protected]

YXTUnsatisfiableConstraintsDetector is available under the MIT license. See the LICENSE file for more info.