检查类responsesToSelector是否不起作用

Question

The following line compiles fine but incorrectly returns false in iOS 8. Why?

[[NSLayoutConstraint class] respondsToSelector:@selector(setActive:)]

However, the following correctly returns true -

[self.heightLayoutConstraint respondsToSelector:@selector(setActive:)]

where self.heightLayoutConstraint is of type NSLayoutConstraint .

Answer 1

setActive: is not a class method on NSLayoutConstraint , so the return value is correct: the class itself does not respond to that selector.

I think you're looking for the class method +instancesRespondToSelector:

[NSLayoutConstraint instancesRespondToSelector:@selector(setActive:)]