聲明 Swift 中的 Auto Layout：Cartography

Cartography 是用來聲明 Swift 中的 Auto Layout，無需輸入任何 stringly 就可設置自己 Auto Layout 的約束聲明。

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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