Rails-SimpleForm：collection中默认选择的单选按钮

= f.association :manufactureType, :collection => ManufactureType.all, :as => :radio

:checked => @manufacture_types[0]

:checked => ManufactureType.first

= f.input :attending, as: :radio_buttons, :collection => [ [\'Yes\', true], [\'No\', false] ], :checked => [\'Yes\', true]

:checked => 1

= f.input :body_format,
  collection: [[\'markdown\', \'Markdown\']],
  label_method: :last,
  value_method: :first,
  as: :radio_buttons,
  checked: \'markdown\', # THIS
  required: true