title: How to access form object parameters in active admin
body: <p>Really hope this is actually possible but I can't seem to access my forms parameters to send with my custom action</p>
  
  <p>My aim here is for a user to fill in their form, click on a Preview button that will show them what their post will look like, i have created the view which is fine, just passing the parameters is an issue.</p>
  
  <p>This is my current form</p>
  
  <pre><code># Create Blog Post
  form do |f|
    inputs 'Blog' do
      f.semantic_errors
      f.input :title
      f.input :category_id, as: :select, collection: Category.all
      f.input :comments, as: :text, input_html: { rows: 10, cols: 10 }
      f.input :published, as: :boolean
    end
    inputs 'Submit' do
      f.actions do
      f.action :submit
      f.action :cancel
      f.action :reset
      li do
        link_to 'Preview', preview_my_admin_panel_posts_path(post: { title: "test", comments: 'comments', category_id: '1' }) # Hardcoded for now
      end
     end
   end
  end
  
  # Collection Action to handle object
  collection_action :preview, method: :get do
    @post = Post.new(permitted_params[:post])
  end
  </code></pre>
  
  <p>So with everything the way it is (hardcoded) the params are passed through and output in my preview view, but as soon as i try accessing the forms object/params nothing gets passed th</p>
  
  <pre><code># Console Output
  1 - link_to 'Preview', preview_my_admin_panel_posts_path(post: { title: f.object.title, comments: f.object.comments, category_id: f.object.category_id})
  #&lt;Post:0x007f8bbe1fc4c0 id: nil, title: "", comments: "", category_id: nil, slug: nil, published: 0, created_at: nil, updated_at: nil&gt;
  2 - link_to 'Preview', preview_my_admin_panel_posts_path(post: { title: f.title, comments: f.comments, category_id: f.category_id })
  # Console Output
  #&lt;Post:0x007f8bbe1fc4c0 id: nil, title: nil, comments: nil, category_id: nil, slug: nil, published: 0, created_at: nil, updated_at: nil&gt;
  3 - link_to 'Preview', preview_my_admin_panel_posts_path(@post)
  # Console Output
  #&lt;Post:0x007f8bbe1fc4c0 id: nil, title: nil, comments: nil, category_id: nil, slug: nil, published: 0, created_at: nil, updated_at: nil&gt;
  </code></pre>
  
  <p>Not sure where else to go with this, f.object.param seems close but passing through empty strings? has anyone done this before ?</p>
  
  <p>If anyone has an alternative solution would love to hear it.</p>
  
  <p>Thanks</p>
  
  <p>Update</p>
  
  <p>When outputting params to the console i get this returned</p>
  
  <pre><code>{"action"=&gt;"preview", "controller"=&gt;"my_admin_panel/posts"}
  </code></pre>