Correct way to delete a NSLayoutConstraint

Question

In my apps I'm working a lot with constraints, in most cases with animations as well. In certain circumstances I need to remove constraints and add new ones.

As I need to support iOS 7 as well, I'm not able to use the active property, which would else be the solution for me.

The way to remove constraints is to use the removeConstraint method on a UIView.

Is it possible to create a method like

constraint.remove()

so you don't have to know which view is taking care over the constraint?

Answer 1

What I do is create arrays of the constraints that I wish to be able to add/remove and simply use the following:

@property NSMutableArray *newConstraints;

Fill up the newConstraints

iOS7 and iOS8:

[self.viewToChange addConstraints:self.newConstraints];
[self.viewToChange removeConstraints:self.newConstraints];

or iOS8 only, use the new mechanism

[NSLayoutConstraint activateConstraints:self.newConstraints];
[NSLayoutConstraint deactivateConstraints:self.newConstraints];

With this you can apply a set, remove the set and apply a new set.

You can also create the initial list from the storyboard set if you can identify which constraints are which.

Answer 2

I've ended up using the method autoRemove provided by the PureLayout library: https://github.com/smileyborg/PureLayout

This method finds the commonSuperview using the firstItem or secondItem and removes the constraint from the correct view.

It resulted in this one liner:

containerTopConstraint.autoRemove()