Paperclip with Rails4 and active admin

admin-projects.rb

ActiveAdmin.register Project do

  # Don't forget to add the image attribute (here thumbnails) to permitted_params
  controller do
    def permitted_params
      params.permit project: [:title, :summary, :description, :thumbnail, :date, :url, :client_list, :technology_list, :type_list]
    end
  end

  form do |f|
    f.inputs "Project Details" do
      f.input :title
      f.input :thumbnail, :as => :file, :hint => f.template.image_tag(f.object.thumbnail.url(:thumb))
      # Will preview the image when the object is edited
    end
    f.actions
  end

  show do |ad|
      attributes_table do
        row :title
        row :thumbnail do
          image_tag(ad.thumbnail.url(:thumb))
        end
        # Will display the image on show object page
      end
    end
end

project.rb

class Project < ActiveRecord::Base
  has_attached_file :thumbnail, :styles => { :medium => "300x300#", :thumb => "200x200#" }
  
  # 200x200# crop the image
  # 200x200> scale the image to 200px wide at maximum keeping aspect ratio
end

YEAH!
Finally get it worked:
Above in "admin-projects.rb" file, 13 line change into:

f.input :thumbnail, :required => false, :as => :file

Also in "project.rb", add extra line :

validates_attachment :thumbnail, content_type: { content_type: ["image/jpg", "image/jpeg",     "image/png"] } 

Thanks for sharing, @jameslafa. The protected params can be written in one line. It doesn't require the controller wrapper or permitted_params method.

permit_params :title, :summary, :description, :thumbnail, :date, :url, :client_list, :technology_list, :type_list

thanks for sharing .... It too simple after I read this doc

I think, f.template on str 13 is unnecessary and may cause weird output like <Class:..>.
It should be
hint: f.template.image_tag(f.object.thumbnail.url(:thumb))

Thanks for your sharing. I am getting some weird message in edit form while using f.template.image_tag. I suggest using image_tag like below:
hint: image_tag(f.object.thumbnail.url(:thumb))

@turkoz yes! Works nice

Your comments were all very useful for me - I thank you.

hyy i need help Active Admin image uploading for product please help me ...