yavfl

yavfl is Yet Anoter Visual Format Language for Auto Layout.

Usage

In yavfl, you can write the code of visual format language as follows:

visualFormat(label, textField) { l, t in
    .v ~ |-40-[l,==32];
    .v ~ |-40-[t,==32];
    .h ~ |-20-[l,==t]-10-[t]-|
}

• Trailing ;s are needed since Xcode 7 beta 3 when you will write multiple statements in a block.

The following code is the equivallent code of the original visual format:

let dic = ["l": label, "t": textField]
label.setTranslatesAutoresizingMaskIntoConstraints(false)
textField.setTranslatesAutoresizingMaskIntoConstraints(false)
let c1 = NSLayoutConstraint.constraintsWithVisualFormat("V:|-40-[l(32)]", options: nil, metrics: nil, views: dic)
let c2 = NSLayoutConstraint.constraintsWithVisualFormat("V:|-40-[t(32)]", options: nil, metrics: nil, views: dic)
let c3 = NSLayoutConstraint.constraintsWithVisualFormat("|-20-[l(==t)]-10-[t]-|", options: nil, metrics: nil, views: dic)
self.view.addConstraints(c1)
self.view.addConstraints(c2)
self.view.addConstraints(c3)

If you aren't familiar with Visual Format Language, please visit the original Visual Format Language page first.

More Examples

Limitations

• Yavfl does not check syntatic validity. You don't expect the code is valid even if its compilation succeeded.
• Connection's predicateList supports only one predicate.
• function visualFormat supports up to 5 views.

Differences from the Original Visual Format Language

Some parts of the syntax are changed due to Swift's syntax limitation.

• Do not use () for view's predicate.
  • Use [button1,==button2] instead of [button1(==button2)].
• Use ~ instead of : for orientation and @ for priority, because these can not be used for custom operators.
  • Use .h ~ |-[view]-| instead of h:|-[view]-|.
  • Use [view,==100~200] instead of [view(==100@200)].
• Orientation (.h or .v) and operator ~ are required for applying layout constraints.
  • Operator ~ is a trigger for creating and applying constraints.
• Connection (-) is required between views.
  • [v1][v2] is not allowed due to the syntax limitation. Use [v1]-0-[v2] instead.
• Relation (==, <= or >=) is required for predicate.
  • [view,100] is not allowed. Use [view,==100] instead.

Install

pod 'yavfl'

Or, just copy yavfl.swift into your project.

Other Resources (in Japanese)

• Blog article
• Slide @ Speaker Deck