From: Joel VanderWerf <vjoel@...>
Date: 2005-10-10T06:44:08+09:00
Subject: Re: Event Handling

iamscottwalter@gmail.com wrote:
> Hi,
> 
> I am coming from the Java world and was wondering if there ins anything
> in Ruby similar to Java's event processing?  For  example I have a
> particular Object that can fire off an event to all objects that listen
> for that event.  A more real world example would be that I have a
> delete() method that was called and I want to let all interested
> parties know that the delete() method was called.
> 
> In the Java space I would setup an event listener.  When the delete()
> method would be called I wouold send an event to all my registered
> listeners.
> 
> I hope I was clear enough.
> 
> 
> Thanks in advance, Scott.
> 

Take look at observable (http://raa.ruby-lang.org/project/observable).
The main use is declaring obervable attributes that other objects can
"hook" code into, to be notified of changes in state. But there is also
a "signal" feature for transient events with multiple observers.

Here's an example from that project's examples dir:

require 'observable'

include Observable
include Observable::Match

module OpenFileExample
  class FilePicker
    signal :file_chosen
    def run
      self.file_chosen = "foo"
    end
  end

  class FileOpener
    def initialize file_picker
      file_picker.when_file_chosen do |file|
        puts "FileOpener: opening file #{file}."
      end
    end
  end

  picker = FilePicker.new
  opener = FileOpener.new(picker)
  picker.run
  p picker.file_chosen  # signal has passed by now

  # Output:
  # FileOpener: opening file foo.
  # nil
end

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407