Showing an uploaded image in the form - activeadmin/activeadmin GitHub Wiki

To show a preview of a form image, use the :hint form parameter, like so (thank to Greg Tangey for this on the mailing list:

f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => image_tag(f.object.cover_page.url) 
  f.input :cover_page_cache, :as => :hidden 
end

Of course you can still do all the processing you are used to from PaperClip or CarrierWave:

f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => image_tag(f.object.cover_page.url(:thumb)) 
  f.input :cover_page_cache, :as => :hidden 
end

Also you can prevent error if image not uploaded yet:

f.inputs "Attachment", :multipart => true do 
  f.input :cover_page, :as => :file, :hint => f.object.cover_page.present? \
    ? image_tag(f.object.cover_page.url(:thumb))
    : content_tag(:span, "no cover page yet")
  f.input :cover_page_cache, :as => :hidden 
end

Remember the :image_cache input to get previews in non-saved records with e.g. CarrierWave. See Ryan's Railscast on CarrierWave for more information.