class Patterns::Observer

Observer -> Object

An Observer class that receives notifications about events from subjects it is observing. Ruby has an Observer module built in to the language, but we will build one to demonstrate how it works and to give it flexibility that we want for this application. This implementation can be inherited or used by itself. For example, it could be an Admin class watching a User class, or it could just be a class called UserObserver. We would simply add this class to whatever subject list we want to observe.

Attributes

last_event[R]

The last event this observer received

last_notification[R]

The last notification this observer received

Public Class Methods

new() click to toggle source

Initializes the observer class

Examples

=> observer = Observer.new

# File app/models/observer/observer.rb, line 21
def initialize
  @last_notification = 'No notifications received'
  @last_event = 'No events received'
end

Public Instance Methods

on_notify(notification, event) click to toggle source

Is called when this function is invoked by a subject

Note: in a real implementation, the event would likely be a complete object or hash, and would contain much more useful information. It would also likely contain a call to a function to do something, like log the event, or execute an event callback. If it does execute an event callback and the callback could possibly block while your main application waits for it to return, it would be a reasonable choice to use asynchronous scheduling, threads, fork a child process, or some other means of asynchronous processing to complete the callback.

  • notification - The notification received from the subclass

  • event - The event received from the subclass

Examples

=> def notify(notification, event)
=>   @observers.each do |observer|
=>     observer.on_notify(notification, event)
=>   end
=> end

# File app/models/observer/observer.rb, line 44
def on_notify(notification, event)
  @last_notification = notification
  @last_event = event
  puts "Notification: #{notification}, Event: #{event}"
end