CAConstraint represents a single layout constraint between two layers. Each
CAConstraint instance encapsulates one geometry relationship between two layers on the same axis.
- macOS 10.5+
Sibling layers are referenced by name, using the name property of each layer. The special name
superlayer is used to refer to the layer's superlayer.
For example, to specify that a layer should be horizontally centered in its superview you would use the following:
A maximum of two relationships must be specified per axis. If you specify constraints for the left and right edges of a layer, the width will vary. If you specify constraints for the left edge and the width, the right edge of the layer will move relative to the superlayer’s frame. Often you’ll specify only a single edge constraint, the layer’s size in the same axis will be used as the second relationship.