# NSLayoutAnchor A factory class for creating layout constraint objects using a fluent API. ``` @MainActor class NSLayoutAnchor where AnchorType : AnyObject ``` ## Overview Use these constraints to programatically define your layout using Auto Layout. Instead of creating [`NSLayoutConstraint`](/documentation/UIKit/NSLayoutConstraint) objects directly, start with a [`UIView`](/documentation/UIKit/UIView), , or [`UILayoutGuide`](/documentation/UIKit/UILayoutGuide) object you wish to constrain, and select one of that object’s anchor properties. These properties correspond to the main [`NSLayoutConstraint.Attribute`](/documentation/UIKit/NSLayoutConstraint/Attribute) values used in Auto Layout, and provide an appropriate [`NSLayoutAnchor`](/documentation/UIKit/NSLayoutAnchor) subclass for creating constraints to that attribute. Use the anchor’s methods to construct your constraint. > Note: > ``doc://com.apple.uikit/documentation/UIKit/UIView`` does not provide anchor properties for the layout margin attributes. Instead, the ``doc://com.apple.uikit/documentation/UIKit/UIView/layoutMarginsGuide`` property provides a ``doc://com.apple.uikit/documentation/UIKit/UILayoutGuide`` object that represents these margins. Use the guide’s anchor properties to create your constraints. ```swift // Creating constraints using NSLayoutConstraint NSLayoutConstraint(item: subview, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leadingMargin, multiplier: 1.0, constant: 0.0).isActive = true NSLayoutConstraint(item: subview, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailingMargin, multiplier: 1.0, constant: 0.0).isActive = true // Creating the same constraints using Layout Anchors let margins = view.layoutMarginsGuide subview.leadingAnchor.constraint(equalTo: margins.leadingAnchor).isActive = true subview.trailingAnchor.constraint(equalTo: margins.trailingAnchor).isActive = true ``` As you can see from these examples, the [`NSLayoutAnchor`](/documentation/UIKit/NSLayoutAnchor) class provides several advantages over using the [`NSLayoutConstraint`](/documentation/UIKit/NSLayoutConstraint) API directly. - The code is cleaner, more concise, and easier to read. - The ``doc://com.apple.uikit/documentation/UIKit/NSLayoutConstraint/Attribute`` subclasses provide additional type checking, preventing you from creating invalid constraints. > Note: > While the ``doc://com.apple.uikit/documentation/UIKit/NSLayoutAnchor`` class provides additional type checking, it is still possible to create invalid constraints. For example, the compiler allows you to constrain one view’s ``doc://com.apple.uikit/documentation/UIKit/UIView/leadingAnchor`` with another view’s ``doc://com.apple.uikit/documentation/UIKit/UIView/leftAnchor``, since they are both ``doc://com.apple.uikit/documentation/UIKit/NSLayoutXAxisAnchor`` instances. However, Auto Layout does not allow constraints that mix leading and trailing attributes with left or right attributes. As a result, this constraint crashes at runtime. For more information on the anchor properties, see in the [`UIView`](/documentation/UIKit/UIView), , or [`UILayoutGuide`](/documentation/UIKit/UILayoutGuide). > Note: > You never use the ``doc://com.apple.uikit/documentation/UIKit/NSLayoutAnchor`` class directly. Instead, use one of its subclasses, based on the type of constraint you wish to create. > > - Use ``doc://com.apple.uikit/documentation/UIKit/NSLayoutXAxisAnchor`` to create horizontal constraints. > - Use ``doc://com.apple.uikit/documentation/UIKit/NSLayoutYAxisAnchor`` to create vertical constraints. > - Use ``doc://com.apple.uikit/documentation/UIKit/NSLayoutDimension`` to create constraints that affect the view’s height or width. > > However, since you access ``doc://com.apple.uikit/documentation/UIKit/NSLayoutAnchor`` objects using the anchor properties of a ``doc://com.apple.uikit/documentation/UIKit/UIView``, , or ``doc://com.apple.uikit/documentation/UIKit/UILayoutGuide``, a correct subclass is automatically provided. ## Topics ### Building constraints [`constraint(equalTo:)`](/documentation/UIKit/NSLayoutAnchor/constraint(equalTo:)) Returns a constraint that defines one item’s attribute as equal to another. [`constraint(equalTo:constant:)`](/documentation/UIKit/NSLayoutAnchor/constraint(equalTo:constant:)) Returns a constraint that defines one item’s attribute as equal to another item’s attribute plus a constant offset. [`constraint(greaterThanOrEqualTo:)`](/documentation/UIKit/NSLayoutAnchor/constraint(greaterThanOrEqualTo:)) Returns a constraint that defines one item’s attribute as greater than or equal to another. [`constraint(greaterThanOrEqualTo:constant:)`](/documentation/UIKit/NSLayoutAnchor/constraint(greaterThanOrEqualTo:constant:)) Returns a constraint that defines one item’s attribute as greater than or equal to another item’s attribute plus a constant offset. [`constraint(lessThanOrEqualTo:)`](/documentation/UIKit/NSLayoutAnchor/constraint(lessThanOrEqualTo:)) Returns a constraint that defines one item’s attribute as less than or equal to another. [`constraint(lessThanOrEqualTo:constant:)`](/documentation/UIKit/NSLayoutAnchor/constraint(lessThanOrEqualTo:constant:)) Returns a constraint that defines one item’s attribute as less than or equal to another item’s attribute plus a constant offset. ### Debugging the anchor --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)