DynamicKVCArrayMixin.rb

framework 'Cocoa'


module DynamicKVCArrayMixin

  def self.included(base)
    base.extend(ClassMethods)
  end

  module ClassMethods

    def attr_collection_accessor( property_name, synchronised = false )
      property_name = property_name.to_s

      # define basic accessors
      attr_reader property_name

      # self.def_method "set#{property_name.capitalize}" do |*args|
      #   backing_store.array = args
      # end

      self.add_indexed_accessors property_name
    end

    def add_indexed_accessors( property_name )

      define_method :"countOf#{property_name.capitalize}" do
        ivar = instance_variable_get "@#{property_name}"
        ivar.count
      end

      define_method :"countOf#{property_name.capitalize}" do
        ivar = instance_variable_get "@#{property_name}"
        ivar.count
      end

      define_method :"objectIn#{property_name.capitalize}AtIndex:" do |index|
        ivar = instance_variable_get "@#{property_name}"
        ivar.objectAtIndex( index )
      end

      define_method :"get#{property_name.capitalize}:range:" do |objects, range|
        ivar = instance_variable_get "@#{property_name}"
        ivar.getObjects(objects, range:range)
      end

      define_method :"insertObject:in#{property_name.capitalize}AtIndex:" do |anObject, index|
        ivar = instance_variable_get "@#{property_name}"
        ivar.insertObject( anObject, atIndex:index)
      end

      define_method :"removeObjectFrom#{property_name.capitalize}AtIndex:" do |index|
        ivar = instance_variable_get "@#{property_name}"
        ivar.removeObjectAtIndex( index )
      end

    end
  end
  
end


class NSArray
  
  def to_index_set
    index_set = NSMutableIndexSet.indexSet
    self.each do |e|
      index_set.addIndex(e)
    end
    NSIndexSet.alloc.initWithIndexSet(index_set)
  end
  
end

test_DynamicKVCArrayMixin.rb

require 'test/unit'
require 'DynamicKVCArrayMixin'


# ideal interface: an attr declared as a collection property (kvc array)
# ideal implementation: storage and kvo taken care of.
class ClassWithCollectionProperty
  include DynamicKVCArrayMixin

  attr_collection_accessor :my_array

  def initialize
    super

    @my_array = []
  end
end


class Test_DynamicKVCArrayMixin < Test::Unit::TestCase 

  def setup
    super
    @c = ClassWithCollectionProperty.new
    puts "created #{@c}"
    puts "ivar: #{@c.instance_variable_get '@my_array'}"
  end

  def test_attr_collection_accessor
    verify_suite
  end
  
  def verify_suite
    exercise_indexed_accessors
    verify_kvo
  end

  def exercise_indexed_accessors
    # check basic getter
    assert_equal [], @c.valueForKey('my_array')
    
    # insert using collection accessor
    @c.insertObject(1, inMy_arrayAtIndex:0)    
    # check array content
    assert_equal [1], @c.valueForKey('my_array')
  end

  def verify_kvo    
    observer = Object.new
    class << observer
      attr_accessor :called
      def observeValueForKeyPath(keyPath, ofObject:object, change:change, context:context)
        puts "#{object} sent a kvo notification"

        self.called = true
      end
    end
    
    @c.addObserver( observer, forKeyPath:'my_array', 
      options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld, context:nil )

    @c.insertObject( 2, inMy_arrayAtIndex: 0)
    assert_equal [2, 1], @c.my_array

    assert_equal observer.called, true
  end

  # directly accessing the object assigned as the collection property shouldn't result in the collection property being affected.
  def test_direct_mutation
    # objc
    @c.my_array.addObject( 1, atIndex: 0)
    assert_equal [1], @c.my_array
    
    # ruby
    @c.my_array << 2
    assert_equal [1,2], @c.my_array
  end
  
end

when i use the mixin in an irb and inspect the dynamically defined methods:

o.methods(true,true).grep /array/
=> [:"replaceObjectInMy_arrayAtIndex:withObjec",
 :"replaceObjectInMy_arrayAtIndex:withObject:",
 :removeMy_arrayAtIndexes,
 :removeObjectFromMy_arrayAtIndex,
 :"insertMy_array:atIndexe",
 :"insertMy_array:atIndexes:",
 :"insertObject:inMy_arrayAtInde",
 :"insertObject:inMy_arrayAtIndex:",
 :"getMy_array:rang",
 :"getMy_array:range:",
 :objectInMy_arrayAtIndex,
 :countOfMy_array,
 :my_array]