SwiftyLayout

SwiftyLayout is a framework that allows to describe layout constraints (ie NSLayoutConstraint) as a simple mathematical formula in a Swift program.

About Version

• SwiftyLayout 3 for Swift 2
• SwiftyLayout 4 for Swift 3

Code Examples

Basic usage

Using the framework, a layout constraint that "the width of the view A is equal to minus 4.0 to 50% of the width of the Views B" follows:

viewA[.Width] == 0.5 * viewB[.Width] - 4.0

This is the same layout constraints with the following code:

NSLayoutConstraint(
    item: viewA, attribute: .Width,
    relatedBy: .Equal,
    toItem: viewB, attribute: .Width,
    multiplier: 0.5, constant: -4.0)

e.g. Aspect ratio

A layout constraint that "the aspect ratio of the view A is 3:4" follows:

viewA[.Width] * 3.0 == viewA[.Height] * 4.0

This is the same layout constraints with the following code:

NSLayoutConstraint(
    item: viewA, attribute: .Width,
    relatedBy: .Equal,
    toItem: viewA, attribute: .Height,
    multiplier: 4.0/3.0, constant: 0.0)

e.g. Specify the priority

The framework has priority specification operator ~ like the following.

innerView[.Leading] == outerView[.Leading] + 4.0 ~ 750.0

This is the same layout constraints with the following code:

var constraint = NSLayoutConstraint(
    item: innerView, attribute: .Leading,
    relatedBy: .Equal,
    toItem: outerView, attribute: .Leading,
    multiplier: 1.0, constant: 4.0)
constraint.priority = 750.0
// -> constraint

Please refer to the code for the sample application and test case, too.

Refrence Guide

ConstraintTerm

ConstraintTerm means a term that contains a view in the right side or the left side of a layout constraint. For example, a ConstraintTerm representing the width .Width of view viewA:

viewA[.Width]

viewA is a UIView instance object, .Width is a NSLayoutAttribute value. ConstraintTerm is defined as a structure such as the following:

public struct ConstraintTerm
{
    let view: UIView?
    let attribute: NSLayoutAttribute
    var multiplier: CGFloat = 1.0
    var constant: CGFloat = 0.0
}

Operators

The following table, CONSTANT means CGFloat value

operator	lhs	rhs	value	semantics
+	ConstraintTerm	CONSTANT	ConstraintTerm	add rhs value to lhs.constant
+	CONSTANT	ConstraintTerm	ConstraintTerm	add lhs value to rhs.constant
-	ConstraintTerm	CONSTANT	ConstraintTerm	subtract rhs value from lhs.constant
*	ConstraintTerm	CONSTANT	ConstraintTerm	multiply rhs value to lhs.multiplier and lhs.constant
*	CONSTANT	ConstraintTerm	ConstraintTerm	multiply lhs value to rhs.multiplier and rhs.constant
/	ConstraintTerm	CONSTANT	ConstraintTerm	divide lhs.multiplier and lhs.constant by rhs value
==	ConstraintTerm	ConstraintTerm	NSLayoutConstraint	create a layout constraint that "lhs is equal to lhs"
==	ConstraintTerm	CONSTANT	NSLayoutConstraint	ditto
==	CONSTANT	ConstraintTerm	NSLayoutConstraint	ditto
<=	ConstraintTerm	ConstraintTerm	NSLayoutConstraint	create a layout constraint that "lhs is less than or equal to lhs"
<=	ConstraintTerm	CONSTANT	NSLayoutConstraint	ditto
<=	CONSTANT	ConstraintTerm	NSLayoutConstraint	ditto
>=	ConstraintTerm	ConstraintTerm	NSLayoutConstraint	create a layout constraint that "lhs is greater than or equal to lhs"
>=	ConstraintTerm	CONSTANT	NSLayoutConstraint	ditto
>=	CONSTANT	ConstraintTerm	NSLayoutConstraint	ditto
~	NSLayoutConstraint	CONSTANT(Float)	NSLayoutConstraint	Change the priority of a layout constraint, and return the constraint

Requirements

• Swift 2.0 (Xcode 7 or later)
• iOS
  • iOS 8 or later / iOS 7 (by coping the source files directly)
• Mac
  • Mac OS X 10.10 or later

Installation

There are two options.

Using Carthage

Using Carthage, it's easy to add SwiftyLayout to the project.

• Add github "fhisa/SwiftyLayout" to your Cartfile.
• Run carthage update
• Add SwiftyLayout.framework in Carthage/Build/iOS to your Xcode project.

Copying source files directly (iOS 7)

• Add this repository as a git submodule:

$ git submodule add https://github.com/fhisa/SwiftyLayout.git PATH_TO_SUBMODULE
// or
$ carthage update --use-submodules

• Then just add references of SwiftyLayout/*.swift to your Xcode project.

TODO

• CocoaPods support

license

SwiftyLayout is released under the MIT license.