A hacky script that takes .xcassets directories and produces a Swift file defining an enum with a case for each image in the asset directories, as well as an UIImage convenience initializer that takes said enum as an argument instead of a string. This enables compiler-checked UIImage initialization returning non-optional images. Inspired by the …

asset_identifiers.rb

require "pathname"

class XCAsset
  def initialize(path, is_root)
    @path = path
    @is_root = is_root

    name = @path.split.last
    @is_container = !(name.to_s =~ /\.imageset$/)

    if @is_container
      @name = name.to_s.sub(".xcassets", "")
      @children = @path.children.select { |child| 
        !(child.to_s =~ /\.appiconset$/) and child.directory?
      }.map { |child| 
        XCAsset.new(child, false) 
      }.sort_by { |asset| asset.container? ? 0 : 1 }
    else
      @name = name.to_s.sub(".imageset", "")
    end
  end

  def name
    @name
  end

  def children
    @children
  end

  def container?
    @is_container
  end

  def root?
    @is_root
  end
end

class StringRenderer
  def render(assets)
    @tablevel = 0
    str = "import UIKit\n\n"
    str += "extension UIImage {"
    @tablevel += 1
    str += "\n#{tabstring}enum AssetIdentifier: String {\n"
    assets.each { |child| 
      if child.container?
        str += render_container(child)
      else
        str += render_identifier(child)
      end
      str += "\n"
    }
    str += "#{tabstring}}"

    str += render_initializers()
    str += "\n}"
  end

  def tabstring
    (0...@tablevel).reduce("") { |x,y| x += "    " }
  end

  def render_container(container)
    @tablevel += 1

    str = "#{tabstring}"
    if container.root?
      str += "/* #{container.name} */"
    else
      str += "// #{container.name}"
    end

    container.children.each { |child|
      str += "\n"
      if child.container?
        str += render_container(child) if child.children.count > 0
      else
        str += render_identifier(child)
      end
    }
    @tablevel -= 1

    str += "\n"
    str
  end

  def render_identifier(asset)
    name_without_spaces = asset.name.sub(" ", "")
    "#{tabstring}case #{name_without_spaces} = \"#{asset.name}\""
  end

  def render_initializers
    str = "\n\n#{tabstring}convenience init!(assetIdentifier: AssetIdentifier) {"
    @tablevel += 1
    str +=  "\n#{tabstring}self.init(named: assetIdentifier.rawValue)"
    @tablevel -= 1
    str += "\n#{tabstring}}"
    str
  end
end

renderer = StringRenderer.new()

srcroot = nil
input_files = []
output_file = nil

ENV.each do |arg|
  key = arg.first
  val = arg.last
  if key =~ /^SCRIPT_INPUT_FILE(?!_COUNT)/ && val =~ /.xcassets$/
    input_files.push val
  elsif key =~ /^SCRIPT_OUTPUT_FILE/
    output_file = val
  elsif key =~ /^SRCROOT/
    srcroot = val
  end
end

if input_files.empty?
  puts "Error: None or improper input files specified."
  exit
end

if output_file == nil
  puts "Error: No output file specified."
  exit
end

asset_folders = input_files.map { |path|
  p = Pathname.new(path)
  XCAsset.new(p, true) 
}

content = renderer.render(asset_folders)

File.open(output_file, 'w+') { |f| f.write(content) }

build_phase.png

generated_assets.png

images.png

usage.png