Custom form helpers

Yes, you can add to the FormBuilder class and get access to the object passed into the form_for. I've done this for a lot of things: dates, times, measurements, etc. Heres an example:

class ActionView::Helpers::FormBuilder  include ActionView::Helpers::TagHelper  include ActionView::Helpers::FormTagHelper  include ActionView::Helpers::FormOptionsHelper  include ActionView::Helpers::CaptureHelper  include ActionView::Helpers::AssetTagHelper  # Accepts an int and displays a smiley based on >, <, or = 0  def smile_tag(method, options = {})    value = @object.nil? ? 0 : @object.send(method).to_i    options[:id] = field_id(method,options[:index])    smiley = ":-|"    if value > 0      smiley = ":-)"    elsif smiley < 0       smiley = ":-("    end    return text_field_tag(field_name(method,options[:index]),options) + smiley  end  def field_name(label,index=nil)    output = index ? "[#{index}]" : ''    return @object_name + output + "[#{label}]"  end  def field_id(label,index=nil)    output = index ? "_#{index}" : ''    return @object_name + output + "_#{label}"  endend

Which you can use like this:

<% form_for @quiz do |f| %>  <%= f.smile_tag(:score) %><% end %>

There are some instance variables created by Rails that you can access in these helper methods:

• @object - the model object specified by the form
• @object_name - the class name of the object
• @template - I think its an instance of the ActionView, you can possibly bypass all the includes I added by calling methods on the template. Haven't tried that yet.
• @options - options passed to the FormBuilder when its created by the form_for call

I wrote the field_id and field_name methods to create these attributes on the HTML input elements the same way the regular helpers do, I'm sure there is a way to tie into the same methods that Rails uses, but I haven't found it yet.

The sky is the limit on what you can do with these helper methods, they simply return strings. You can create entire HTML tables or pages in one, but you better have a good reason to.

This file should be added in the app/helpers folder

@Tilendor, thanks so much for the pointers. Here is an example of an enum_select form tag helper that uses Rails 4.1 enums to automatically populate the options of a select tag:

# helpers/application_helper.rbmodule ApplicationHelper  class ActionView::Helpers::FormBuilder    # http://stackoverflow.com/a/2625727/1935918    include ActionView::Helpers::FormTagHelper    include ActionView::Helpers::FormOptionsHelper    def enum_select(name, options = {})      # select_tag "company[time_zone]", options_for_select(Company.time_zones      #   .map { |value| [value[0].titleize, value[0]] }, selected: company.time_zone)      select_tag @object_name + "[#{name}]", options_for_select(@object.class.send(name.to_s.pluralize)        .map { |value| [value[0].titleize, value[0]] }, selected: @object.send(name))    end  endend

The trickiest construct is @object.class.send(name.to_s.pluralize) which produces a hash of available values (e.g., Company.time_zones). Putting it in helpers/application_helper.rb makes it automatically available. It is used like:

<%= f.label :billing_status %>:<%= f.enum_select :billing_status %><br />

Our app was displaying phone numbers in text fields, and we wanted to omit the country code for domestic numbers. I was using form helpers. After reading this and rails source a bit, i came to this solution:

class ActionView::Helpers::FormBuilder  def phone_text_field name, options = {}    value = object.public_send(name).to_s    if value.start_with? "9" # national number      value = value[1..-1]      options["value"] = value    end    text_field name, options  endend

I put this on app/helpers/application_helper.rb and use it like i use text_field() helper. Hope this helps someone.