AppObserver.rb Review

[Jim]

Here's my version of a global AppObserver for review and comments. My goal is to create a AppObserver that is general in nature and is available for any plugin that needs it.

Users (other scripts in this context) can use it by require'ing the ruby file, and then registering themselves to the instance.

It uses the singleton.rb file from the Ruby language installation. This guarantees there is only 1 instance of the observer.

Here's a small plugin that shows how it might be used (based on Rick's Select at Startup.) Basically, your plugin registers with the AppObserver and implements the same methods as an AppObserver would (i.e. onNewmodel, onOpenModel, onQuit)

require "app_observer.rb"

module SelectToolAtStartup
  def self.onNewModel(args)
    Sketchup.send_action "selectSelectionTool;"
  end
  def self.onOpenModel(args)
    Sketchup.send_action "selectSelectionTool;"
  end
  AppObserver.instance.register self
end

The AppObserver handles attaching and detaching itself to the model. All a plugin needs to do is require and register itself to the AppObserver. If there is no plugins that register, AppObserver is never attached. When a plugin registers, the AppObserver attaches itself. When all plugins unregister, the AppObserver also detaches itself. (I'm not sure this is a needed optimization.)

And here's the app observer:

require "sketchup"
require "singleton"

class AppObserver < Sketchup;;AppObserver
  include Singleton
  @attached = false

  def onNewModel(*args)
    attach 
    @q.each { |o| o.onNewModel(args) }
  end

  def onOpenModel(*args)
    attach
    @q.each { |o| o.onOpenModel(args) }
  end

  def onQuit(*args)
    @q.each { |o| o.onQuit(args) }
  end

  def attach
    Sketchup.add_observer(self)
    @attached = true
  end
  private ;attach

  def detach
    Sketchup.remove_observer(self)
    @attached = false
  end
  private ;detach

  def register(o)
    attach unless @attached
    @q ||= []
    @q.push o unless @q.include? o
  end

  def unregister(o)
    @q.delete(o)
    detach if @q.empty?
  end

end # class AppObserver

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app_observer.rb