Customizing filter form fields

The filter form builder looks for custom input fields as ActiveAdmin::Inputs::Filter#{as_option.camelize}Field.

Here's an example taken from the mailing list:

# Somewhere, in an initializer or just straight in your activeadmin file:
class ActiveAdmin::Inputs::FilterIsArchivedInput < ActiveAdmin::Inputs::FilterSelectInput
  def input_options
    super.merge include_blank: 'All'
  end

  def collection
    [ ['Live', 'true'], ['Archived', 'false'] ]
  end
end

# In activeadmin
filter :archived, as: :is_archived

Read more about custom inputs in the formtastic documentation and check out the other filter inputs in lib/active_admin/inputs to learn more.