How To: Make a Custom Form Field

In this example, we'll be making a custom form field to capture price and currency values that could be used with the money-rails gem.

Create a new app/fields/monetize_field.rb file and add the following contents:

class MonetizeField < Trestle::Form::Field
  def field
    content_tag :div, class: 'input-group' do
      safe_join [
        content_tag(:span, builder.object.send(name).currency.symbol, class: 'input-group-addon'),
        builder.raw_text_field(name, {class: 'form-control'}),
        builder.raw_select("#{name}_currency", ['USD','GBP'], {}, {class: 'form-control', style: '-webkit-appearance:none;'})        
      ]
    end
  end
end

Then let trestle know about it in config/initializers/trestle.rb:

Trestle.configure do |config|
  # Register a form field type to be made available to the Trestle form builder.
  # Field types should conform to the following method definition:
  #
  # class CustomFormField
  #   def initialize(builder, template, name, options={}, &block); end
  #   def render; end
  # end
  #
  # config.form_field :custom, CustomFormField
  config.form_field :monetize, MonetizeField

  # ...
end

Then in your resource config file (i.e. app/admin/blackmails.rb)

Trestle.resource(:blackmails) do
  form do |blackmail|
    text_field :victim
    text_field :dirt
    monetize :price
  end
end