purplish_layout – a RubyMotion wrapper for Auto Layout on iOS and OS X

About

Ruby lends itself to creating a nice DSL for Auto Layout, so why not? I have been using this for both iOS and OS X apps since mid-2014.

Usage

Use it with visual format strings:

['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
  celf.h '|[l]|'
  celf.v '|-m-[l]-m-|', {'m' => 7}
end

You can also create constraint objects yourself. This is equivalent to the previous example:

['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
  celf.left = l.left
  celf.right = l.right
  l.top = celf.top + 7
  l.bottom = celf.bottom - 7
end

Send #constraints with a block to an array with an even number of elements. They should be pairs – the name (a String) to be used in the format strings in the block, followed by the view it represents.

If there are n views involved, there should be n*2 elements in the array. The block takes n+1 arguments, and the last object is the dictionary mapping generated from the array (usually unused) and the rest of the elements are constraint proxy objects representing each view, in the order specified in the array.

To avoid confusion, it's best to keep the variable names in the block the same as the string names in the array. This syntax can be improved when Proc#parameters is available.

With the exception of the first view listed in the array, translatesAutoresizingMaskIntoConstraints is automatically set to false for every view, so you'll want to specify the outermost view as the first pair.

A multipler can be supplied:

  l.width = celf.width * 0.5

The attributes are available as :left, :right, :top, :bottom, :leading, :trailing, :width, :height, :center_x, :center_y and :baseline.

You can mix the 2 creation methods:

['celf', inner_view, 'l', post_count_label].constraints do |celf, l, _|
  celf.left = l.left
  celf.right = l.right
  celf.v '|-m-[l]-m-|', {'m' => 7}
end

There are 2 attributes in the constraint proxies that you would occasionally find useful:

last_constraint returns the last NSLayoutConstraint created. It's useful if you want to hold on to a NSLayoutConstraint and modify it in an animation.
next_priority sets the priority for the next NSLayoutConstraint you create.

Installation

Add this to your Gemfile: gem 'purplish-layout'
Run bundle install

Dependencies

weak_attr_accessor

License