[code] Detecting when a user changes the axes

Developers Ruby API
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1

This is an example of a simple hybrid observer that detects when the singleton Axes object is changed.

# encoding: UTF-8
#
# A simple Axes Observer to detect when a user changes axes.

module Author
  class AxesSpy < Sketchup::EntityObserver
    
    @@instance ||= self::new

    def self::attach( mod = Sketchup.active_model )
      mod.axes.add_observer(@@instance)
    end

    def onNewModel(mod)
      self::attach(mod)
    end
    alias_method :onOpenModel, :onNewModel

    def expectsStartupModelNotifications()
      true
    end

    def onChangeEntity(ent)
      puts "AxesSpy: #{ent.inspect} changed for #{ent.model.inspect}."
    end

    Sketchup.add_observer(@@instance)

  end
end

* Note that the Axes object was first exposed with SketchUp 2016.

Edit: Fixed alias_method call. args were swapped, in error.
(I always seem to get them backwards. I always think “alias this as that”,
but it is more like “newalias that of this”.)

2

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