Ruby Observer Existence Check

[hank]

Is there any way to check to see if an entity already has an observer attached to it?

I am using:

class MyInstanceObserver < Sketchup;;InstanceObserver
  def onChangeEntity(entity)
	  #puts "onChangeEntity; #{entity}"
  end
end

and then

my_openings = ent.grep(Sketchup;;ComponentInstance).find_all {|oi| oi.definition.name.include?('OPENING') }
  my_openings.each do |oi|
    next unless oi.valid?
  oi.add_observer(MyInstanceObserver.new)
end

But would prefer not to blindly attached an observer always. This loop will have been run previously.

[TIG]

How about doing it this way.
Outside of any of your methods...

@@obs = MyInstanceObserver.new() unless @@obs

That only runs once and its reference can then be used thus:

oi.remove_observer(@@obs) oi.add_observer(@@obs)

Attempting to remove a non-existent observer does NOT raise an error.
So in this way just one instance of the observer is only ever attached to an instance.

[hank]

Thanks TIG. I though @@ was for classes???

I got an "uninitialized class" error until changed @@obs to @obs

Your solution worked perfect though!

[TIG]

You usually set @@obs = nil inside a class [outside of any method].
Then within one of that class's methods [like initialize()] you can set it to be a proper reference - but just the once.
In a class it needs to be @@obs = ... to persist across instances of the class.
A @obs = ... in a class only exists during that one instance of the class.

In my example I set it only if it's not already set [i.e. it is nil].

You can set @obs = ... within a module, outside of any of its methods and that then persists thereafter.

Since I didn't have your whole code I guessed...

[hank]

Thanks TIG. Have not gotten very advanced with Classes etc. so just a simple module. Appreciate the explanation.

[Dan Rathbun]

@tig said:

You can set @obs = ... within a module, outside of any of its methods and that then persists thereafter.

This is true because, a module is an instance of class Module.

@hank said:

Have not gotten very advanced with Classes etc. so just a simple module.

The Class class is the direct child class of class Module. So classes inherit all of Module's functionality, and get a little bit of their own (ie, a few extra methods and the ability to have many instance copies of themselves, that can hold their own instance variable values.)