Temporarily remove NSLayoutConstraint?

Question

I have a UITableViewCell subclass laid out using AutoLayout, and I’d like a small animation in which the image view transforms, grows a bit and shrinks back.

At present, due to the constraints, the labels on the right side of the image are moving too (as they should be).

I’d like a quick and easy means to temporarily say “leave those labels where they currently are while this animation is running”. Is that something I can do without needing to remove and re-add those constraints, which is a lot of hassle?

Answer 1

Starting in iOS 8 NSLayoutConstraints now have an active property that you can change myConstraint.active = NO;. This removes the constraint, while setting this value to YES will [re]add it:

Activating or deactivating the constraint calls addConstraint: and removeConstraint: on the view that is the closest common ancestor of the items managed by this constraint. Use this property instead of calling addConstraint: or removeConstraint: directly. source

Additionally, there are two new class methods activateConstraints: and deactivateConstraints: that take an array of constraints (NSArray<NSLayoutConstraint>), so that can be helpful, especially if you have an IBOutletCollection with constraints.

[NSLayoutConstraint deactivateConstraints:myConstraints];

Answer 2

There's no API to say "leave these views here", temporarily disabling some parts of the autolayout. There are several possible solutions:

• remove your constraints during animation
• arrange your constraints differently (making them to a superview of the image view, for example, or having them only depend on the center of the image view)
• override layoutSubviews of a container view to stick your labels back where you want them after autolayout runs in [super layoutSubviews] (or remove the transform of your image view, run autolayout and then put it back)
• subclass your image view and override frameForAlignmentRect: and alignmentRectForFrame: to get autolayout to use the untransformed frame for alignment purposes.

More details and suggestions are available in the answers here, which is a similar question of how to make transforms and autolayout play together: How do I adjust the anchor point of a CALayer, when Auto Layout is being used?