问题
Im useing joomla 2.5, and I want to create a custom form field type that stored in the same module.
In the XML:
 <fieldset  name="basic" addfieldpath="/modules/mod_royalslider/fields"></fields>
      <fieldset name="basic">
           <field name="title" type="City" label="anythging" description=""   />
      </fieldset>
 </fields>
In the file /modules/mod_royalslider/fields/city.php
<?php
// Check to ensure this file is included in Joomla!
defined('_JEXEC') or die('Restricted access');
jimport('joomla.form.formfield');
class JFormFieldCity extends JFormField {
    protected $type = 'City';
    // getLabel() left out
    public function getInput() {
            return '<select id="'.$this->id.'" name="'.$this->name.'">'.
                   '<option value="1" >New York</option>'.
                   '<option value="2" >Chicago</option>'.
                   '<option value="3" >San Francisco</option>'.
                   '</select>';
    }
}
for now it show me error, when ever i remove 
 <fieldset  name="basic" addfieldpath="/modules/mod_royalslider/fields"></fields>
the error gone and the field disply as a text field.
回答1:
You forgot to specify models in the addfieldpath
<fields name="params">
   <fieldset name="basic" addfieldpath="/modules/mod_royalslider/models/fields">
       <field name="title" type="City" label="anythging" description=""   />
   </fieldset>
</fields>
Just put the fields folder inside the models folder and put the path like above.
回答2:
You just do it using the code you gave, easy:
 <fields>
      <fieldset name="basic" addfieldpath="/modules/mod_royalslider/fields">
           <field name="title" type="City" label="anythging" description=""   />
      </fieldset>
 </fields>
回答3:
Use addfieldpath within fields as like ::
<fields name="params" addfieldpath="/modules/mod_royalslider/models/fields" >
       <fieldset name="basic">
         <field name="title" type="City" label="anything" description="" />
       </fieldset>
 </fields>
回答4:
you can try using this code. this work in mine
<fieldset addfieldpath="/modules/mod_royalslider/models/fields" name="basic">
   <field name="title" type="City" label="anything" description=""  />
</fieldset>
来源:https://stackoverflow.com/questions/14197236/how-to-create-a-custom-form-field-type-in-a-module