Ruby on Rails: instance & class variables not maintaining value in controller

Question

at the top of my controller, outside of any method, I have

    @@javascript_is_disabled = false

and I have methods that that the view calls and invokes something like this

    @@javascript_is_disabled = params[:javascript_disabled]

but when I need the @@javascript_is_disabled in completely different method.. it is always false.

I know it changes in the method with params args... cause those methods behave differently, and appropriately

And ideas?

Daniel Beardsley · Accepted Answer · 2010-06-15 18:36:44Z

The variable @@javascript_is_disabled is a class variable and it refers to a different thing depending on where you access it from. From within the Controller class body it doesn't refer to the same thing as when you use it from within a controller method or a view. This is actually a pretty complex subject involving Eigenclasses

I suggest implementing it using a view helper or a protected method:

protected

attr_writer :javascript_is_disabled
def javascript_is_disabled
  # Replace false with your intended default value
  @javascript_is_disabled.nil? ? false : @javascript_is_disabled
end

Then you can reference it from within your views and controller action methods like an attribute javascript_is_disabled = true or if javascript_is_disabled ...

You could also leave out the attr_writer ... part and just always remember to assign values to the instance variable @javascript_is_disabled = ...

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