Setting Runtime Attributes in NSLayoutConstraint

Question

I would like to set the property identifierto a few of my limitations from the inline interface. I used the table User Defined Runtime Attributesin IB before with instances NSView, and I had no problems, but I do not do the same with restriction classes anywhere. When I try to access the identifier in the code, it simply returns null, not the row entered in the Value column of the table. I suppose this might be due to the xib loading mechanism, but I hope someone can tell with certainty what the problem is.

IB --> Identity Inspector --> User Defined Runtime Attributes:

• Key path : identifier
• Type : string
• Value : TextViewWidthConstraint

later in IBAction:

NSLog(@"%@", self.widthCon.identifier);

// --> (null)

Answer 1

In the NSLayoutConstraint implementation, something seems to be wrong. Creating a category in NSLayoutConstraint and rewriting some methods for debugging purposes revealed the following:

Runtime attributes must be removed by Xcode at compile time for the following reasons:

• The rewritten KVC methods are inside NSLayoutCategory setValue:forKey:, setValue:forKeyPath:and are setValue:undefinedKey:never called.

• The rewritten method setIdentifier:is called but never gets the passed value from the runtime attribute section

• Providing invalid keys does not create errors, as on any other object, such as NSView:

  2014-03-19 08: 25: 52.806 LayoutTestApp [13733: 303] [setValue: forUndefinedKey:]: testKey.

, NSLayoutConstraint Xcode ( init ). , Apple NSLayoutConstraints . : , , atm.

Answer 2

, NSLayoutConstraint identifier, :

NSLog(@"%@", [self.widthCon valueForKey:@"identifier"]);