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.)