---
title: CAConstraintLayoutManager
framework: quartzcore
role: symbol
role_heading: Class
path: quartzcore/caconstraintlayoutmanager
---

# CAConstraintLayoutManager

An object that provides a constraint-based layout manager.

## Declaration

```swift
class CAConstraintLayoutManager
```

## Overview

Overview You use the shared instance of this object by assigning it to the layoutManager property of any layer objects to which you have added constraints. During a layout update, Core Animation uses the layout manager to update the size and position of the sublayers based on the registered set of constraints. Constraints let you define a set of geometric relationships between a layer and its sibling layers or between a layer and its superlayer. These relationships are expressed using constraint objects, which are instances of the CAConstraint class. When creating constraints, you can reference a layer by name using that object’s name property. You can also use the special name superlayer to refer to the layer’s superlayer. The following example shows how you can use CAConstraintLayoutManager to create a layer containing two constrained sublayers: leftLayer and rightLayer. A series of CAConstraint objects are created so that the sublayers match their superlayer’s height and are half of its width. leftConstraint matches the CAConstraintAttribute.minX attribute and rightConstraint matches the CAConstraintAttribute.maxX attribute. The end result is that the two sublayers are always laid out so that leftLayer fills the left half of layer and rightLayer fills the right half of layer. let layer = CALayer() let heightConstraint = CAConstraint(attribute: .height,                                     relativeTo: "superlayer",                                     attribute: .height)      let widthConstraint = CAConstraint(attribute: .width,                                    relativeTo: "superlayer",                                    attribute: .width,                                    scale: 0.5,                                    offset: 0)       let leftConstraint = CAConstraint(attribute: .minX,                                   relativeTo: "superlayer",                                   attribute: .minX)       let rightConstraint = CAConstraint(attribute: .maxX,                                    relativeTo: "superlayer",                                    attribute: .maxX)      let bottomConstraint = CAConstraint(attribute: .minY,                                     relativeTo: "superlayer",                                     attribute: .minY)          let leftLayer = CALayer() leftLayer.frame = CGRect(x: 0, y: 0, width: 20, height: 20) layer.addSublayer(leftLayer) leftLayer.constraints = [heightConstraint, widthConstraint,                           leftConstraint, bottomConstraint] leftLayer.backgroundColor = NSColor.red.cgColor    let rightLayer = CALayer() layer.addSublayer(rightLayer) rightLayer.constraints = [heightConstraint, widthConstraint,                            rightConstraint, bottomConstraint] rightLayer.backgroundColor = NSColor.blue.cgColor      layer.layoutManager = CAConstraintLayoutManager() important: It is possible to specify a set of constraints that will cause layout to fail. For example, layout may fail if your constraints contain a circular dependency. When that happens, the behavior of the layout manager is undefined. This class is not meant to be subclassed.

## Relationships

### Inherits From

- [NSObject](objectivec/nsobject-swift.class.md)

### Conforms To

- [CALayoutManager](quartzcore/calayoutmanager.md)
- [CVarArg](swift/cvararg.md)
- [CustomDebugStringConvertible](swift/customdebugstringconvertible.md)
- [CustomStringConvertible](swift/customstringconvertible.md)
- [Equatable](swift/equatable.md)
- [Hashable](swift/hashable.md)
- [NSObjectProtocol](objectivec/nsobjectprotocol.md)

## See Also

### Layer Basics

- [CALayer](quartzcore/calayer.md)
- [CALayerDelegate](quartzcore/calayerdelegate.md)
- [CAConstraint](quartzcore/caconstraint.md)
- [CALayoutManager](quartzcore/calayoutmanager.md)
- [CAAction](quartzcore/caaction.md)