Introduction

You can activate or deactivate Auto Layout constraints whenever your view hierarchy and layout state require it, but the real rule is to do it at state boundaries, not randomly. In practice that usually means activating constraints during setup, then toggling them later only when the UI changes mode, size, or visibility.

Activate Constraints During View Setup

The most common time to activate constraints is when you create or configure the views.

1NSLayoutConstraint.activate([
2    titleLabel.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor, constant: 16),
3    titleLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 16)
4])

This is the right place for constraints that define the normal layout of the screen.

Deactivate and Activate Constraints When the Layout Mode Changes

A common reason to toggle constraints is that the UI has two valid layouts, such as compact versus expanded mode.

NSLayoutConstraint.deactivate(compactConstraints)
NSLayoutConstraint.activate(expandedConstraints)

That is cleaner than mutating dozens of constants when the layout relationship itself changes.

Animate Constraint Changes Deliberately

If the layout should animate, toggle the relevant constraints and then call layoutIfNeeded inside an animation block.

1UIView.animate(withDuration: 0.3) {
2    NSLayoutConstraint.deactivate(self.compactConstraints)
3    NSLayoutConstraint.activate(self.expandedConstraints)
4    self.view.layoutIfNeeded()
5}

This is a common and correct pattern for animated Auto Layout transitions.

Avoid Constant Constraint Churn

Constraints are not meant to be created and destroyed casually on every layout pass. If the layout relationship stays the same and only spacing changes, updating a constant is often better than deactivating and recreating constraints.

The goal is to change the smallest thing that actually changed.

Common Pitfalls

• Activating constraints before the involved views are properly in the hierarchy or configured for Auto Layout.
• Deactivating constraints without activating a replacement set, leaving the layout ambiguous.
• Recreating constraints repeatedly when updating a constant would have been enough.
• Toggling constraints without calling layout updates when an animated transition is expected.
• Treating Auto Layout changes as ad hoc code instead of as explicit UI state transitions.

Summary

• Activate constraints during setup for the default layout.
• Toggle constraints when the UI genuinely changes layout mode.
• Use layoutIfNeeded for animated transitions.
• Update constants instead of replacing constraints when only spacing changes.
• Treat constraint activation and deactivation as state management, not random view tweaking.