gmap4rails in ActiveAdmin: maps does not appear - ruby-on-rails

Question

In try to use gmaps4rails in my ActiveAdmin / Rails app. To do so, I have added the following in my Gemfile:
gem 'gmaps4rails'
and ran a "bundle". I updated the 'show' method in app/admin/device.rb file with:
show do
attributes_table do
row :name
end
# Get device location
#markers = Location.all.to_gmaps4rails
div do
render "map"
end
end
In the app/views/admin/devices/_map.html.erb I have the following code:
<%= stylesheet_link_tag 'gmaps4rails' %>
<%= gmaps4rails(#markers) %>
<%= yield :scripts %>
In app/assets/javascripts/application.js:
//= require gmaps4rails/gmaps4rails.googlemaps
//= require gmaps4rails/gmaps4rails.base
//= require jquery
//= require jquery_ujs
//= require_tree .
And in my app/models/location.rb:
class Location < ActiveRecord::Base
acts_as_gmappable
attr_accessible :latitude, :longitude
def gmaps4rails_address
"#{self.latitude}, #{self.longitude}"
end
def location
[:latitude, :longitude]
end
end
When I go on the show page of a device, the map does not shows up (all blank). Is there any configuration I missed ?
UPDATE
I have checked with chrome developer tools and noticed the following error:
Uncaught SyntaxError: Unexpected token ;
that make reference to the line:
Gmaps.map.markers = ;

Answer 1

Fix with the following:
div do
markers = Location.all.to_gmaps4rails
render "map", { :markers => markers }
end
and :
<%= stylesheet_link_tag 'gmaps4rails' %>
<%= gmaps({
"map_options" => { "zoom" => 2, "auto_adjust" => false},
"markers" => { "data" => markers }
})
%>
<%= yield :scripts %>

Answer 2

You have to load the Javascript files in the /config/initializers/active_admin.rb; search for the section:
# To load a javascript file:
# config.register_javascript 'my_javascript.js'
Also, I think you should add the CSS files (if is not appearing) into the same file.
Remember that ActiveAdmin manages its own Javascript file, named active_admin.js; you can try loading the Javascript files in this JS; some time ago I had a similar problem and I only was able to solve it adding the files in the initializer.