Lane Assist

An Assistant for AutoLayout in Swift

You know the problem: you just want to set a NSLayoutConstraint in your Code and you end up with something like this:

addConstraint(NSLayoutConstraint(item: view, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 0))

Wouldn’t it be nice to write something more swift-like and readable? Like this:

view.LA.setTop.addToSuperview()

With Lane Assist you can! Just add Lane Assist to your project and you’re done. Lane Assist is not a DSL on top of AutoLayout that you have to learn, instead it just creates basic NSLayoutConstraints with some easy function calls. Method chaining makes it even more comfortable to use.

Installation

You can copy and add the LaneAssist/LaneAssist.swift file manually to your project to use it. If your project is targeting iOS 7, this is the only possible way.

Usage

Standard Layout variables

• setWidth
• setHeight
• setTop
• setBottom
• setLeft
• setRight
• setCenterX
• setCenterY
• setBaseline

These variables are optionals. If you haven’t added your view to the view hierarchy it will return nil!

Relation Methods

• equalTo()
• greaterThanOrEqual()
• lessThanOrEqual()

Attribute Methods

• toBaseline()
• toLeft()
• toRight()
• toTop()
• toBottom()
• toCenterX()
• toCenterY()
• toWidth()
• toHeight()
• toBaseline()
• toCenterXWithinMargins()
• toCenterYWithinMargins()
• toFirstBaseline()
• toLeading()
• toLeadingMargin()
• toLeftMargin()
• toRightMargin()
• toTopMargin()
• toBottomMargin()
• toTrailing()
• toTrailingMargin()

Other Methods

• ofView(view: UIView)
• ofSelf()
• withMultiplier(multiplier: CGFloat)
• withConstant(constant: CGFloat)
• setFixed(constant: CGFloat)
• withPriority(priority: UILayoutPriority)

Methods to add a constraint to a view

• addToSuperview()
• addToView(view: UIView)
• addToSelf()

How it works

You can easily chain all the properties after each other. First you start with a view and geht the Lane Assist Object view.LA, this will set your views translatesAutoresizingMaskIntoConstraints to false. Then you choose your initial value to set, for example top view.LA.setTop and now you can easily chain all the methods that are available, for example view.LA.setTop.toBottom().ofView(otherView).withConstant(10).withPriority(42).addToSuperview().

More examples

The usual NSLayoutConstraint code to place a view horizontally centered, 100px from top, with the same width as the superview and the same height as the view’s width:

addConstraint(NSLayoutConstraint(item: view, attribute: .CenterX, relatedBy: .Equal, toItem: self, attribute: .CenterX, multiplier: 1, constant: 0))
addConstraint(NSLayoutConstraint(item: view, attribute: .Top, relatedBy: .Equal, toItem: self, attribute: .Top, multiplier: 1, constant: 100))
addConstraint(NSLayoutConstraint(item: view, attribute: .Width, relatedBy: .Equal, toItem: self, attribute: .Width, multiplier: 1, constant: 0))
addConstraint(NSLayoutConstraint(item: view, attribute: .Height, relatedBy: .Equal, toItem: view, attribute: .Width, multiplier: 1, constant: 0))

The same code using Lane Assist:

view.LA.setCenterX.addToSuperview()
view.LA.setTop.withConstant(100).addToSuperview()
view.LA.setWidth.addToSuperview()
view.LA.setHeight.toWidth().ofSelf().addToSuperview()

To hold on to a constraint (for example if you want to animate it), just assign it to a variable. Let’s say we want to animate the top-constraint:

let topConstraint = view.LA.setTop.withConstant(100).addToSuperview()
self.layoutIfNeeded()

UIView.animateWithDuration(2, animations: { () -> Void in
    self.topConstraint.constant = 200
    self.layoutIfNeeded()
})

⚠️ Per default Lane Assists sets translatesAutoresizingMaskIntoConstraints to false on your view, if used.

Lane Assist is currently used in real world Projects by me. If you end up using Lane Assist in your projects too, I’d happy to hear your thoughts and ideas. You can reach me through Twitter.