floriankrueger/cartography

Declarative Auto Layout in Swift

Cartography

Set up your Auto Layout constraints declaratively and without any stringly typing!

How to use

Call the layout function with your UIView or NSView instances as well as a closure in which you declare the constraints between the different attributes of your views:

layout(view1, view2) { view1, view2 in
    view1.width   == (view1.superview!.width - 50) * 0.5
    view2.width   == view1.width - 50
    view1.height  == 40
    view2.height  == view1.height
    view1.centerX == view1.superview!.centerX
    view2.centerX == view1.centerX

    view1.top >= view1.superview!.top + 20
    view2.top == view1.bottom + 20
}

Supported attributes

Cartography supports all built-in attributes as of iOS 7 and OS X 10.9, those are: width, height, top, right bottom, left, leading, trailing, centerX, centerY and baseline. These can be further refined using the following operators: *, /, + and -.

Additionally, it supports convenient compound attributes that allow you to assign multiple attributes at once:

layout(view) { view in
    view.size   == view.superview!.size / 2
    view.center == view.superview!.center
}

layout(view) { view in
    view.edges == inset(view.superview!.edges, 20, 20, 40, 20); return
}

(We need to return explicitly here to work around a bug in Swift, this only affects single line blocks, however.)

Setting priorities

You can set the priorities of your constraints using the ~ operator:

layout(view) { view in
    view.width  >= 200 ~ 100
    view.height >= 200 ~ 100
}

Capturing constraints

Since the ==, >=, <= and ~ emit NSLayoutConstraint instances, you can capture their results if you need to refer to the layout constraints at a later time:

var width: NSLayoutConstraint?

layout(view) { view in
    width = (view.width == 200 ~ 100); return
}

Note that declaring compound attributes returns multiple constraints at once:

var constraints: NSLayoutConstraint[]?

layout(view) { view in
    constraints = (view.size == view.superview!.size ~ 100); return
}

About Cartography

Cartography is written in Swift so it's pretty much beta by definition. It was inspired by the excellent FLKAutoLayout by Florian Kugler.