声明 Swift 中的 Auto Layout：Cartography

Cartography 是用来声明 Swift 中的 Auto Layout，无需输入任何 stringly 就可设置自己 Auto Layout 的约束声明。

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   == (view.superview!.width - 50) * 0.5      view2.width   == view1.width - 50      view1.height  == 40      view2.height  == view1.height      view1.centerX == view.superview!.centerX      view2.centerX == view1.centerX        view1.top >= view.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)  }

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)  }

Note that declaring compound attributes returns multiple constraints at once:

var constraints: NSLayoutConstraint[]?    layout(view) { view in      constraints = (view.size == view.superview!.size ~ 100)  }

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