Key-Value-Observing for RubyMotion

A domain specific language (DSL) for easy use of key-value-observing (KVO) in RubyMotion projects.

If you'd like to learn more about the KVO mechanism on iOS and Mac, take a look at the Key-Value Observing Programming Guide by Apple.

	Note: Although the classes of the UIKit framework generally do not support KVO, you can still implement it
	in the custom objects of your application, including custom views.

Getting started

Add motion-kvo as a git submodule of your RubyMotion project:

git clone https://github.com/dreimannzelt/motion-kvo.git vendor/motion-kvo

Add the motion-kvo lib path to your project 'Rakefile'

Motion::Project::App.setup do |app|
  app.name = 'MyApp'
  app.files.unshift(Dir.glob(File.join(app.project_dir, 'vendor/motion-kvo/lib/**/*.rb')))
end

Now you can start to add the helper methods to every class you like:

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	...
end

Register observers

To observe a key path of a target you do:

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	def viewDidLoad
		@label = create_ui_label()
		
		observe(@label, "text") do |old_value, new_value|
			puts "Changed #{old_value} to #{new_value}"
		end
	end
	
end

It's possible to add more than one block to the same key path:

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	def viewDidLoad
		@label = create_ui_label()
		
		observe(@label, "text") do |old_value, new_value|
			puts "Hello from viewDidLoad!"
		end		
	end
	
	def viewDidAppear(animated)
		observe(@label, "text") do |old_value, new_value|
			puts "Hello from viewDidAppear!"
		end
	end
	
end

You can also observe collections (WORK IN PROGRESS):

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	attr_accessor :items
	
	def viewDidLoad
		@table_view = create_ui_table_view()
		@items = [ ]
		
		observe(self, "items") do |old_value, new_value, indexes|
			@table.reloadData
		end
	end
	
end

Unregister observers

You are responsible to unregister observers properly. You can unregister one observer:

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	...
	
	def viewWillDisappear(animated)
		unobserve(@label, "text")
	end
	
end

or all at once:

class ExampleViewController < UIViewController
	include Dreimannzelt::KVO
	
	...
	
	def viewWillDisappear(animated)
		unobserve_all
	end
	
end

License

motion-kvo is released under the MIT license:

http://www.opensource.org/licenses/MIT