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Creating a custom form field type

From Joomla! Documentation

Revision as of 11:38, 7 June 2011 by Mvangeest (Talk | contribs)

JForm, a feature introduced in Joomla 1.6, lets you easily create HTML forms (<form>). Forms created using JForm consist of form fields, implemented as JFormFields. There is a JFormField for each different field type you can find in a form, such as a text field type and a date field type. JForm supports a large selection of standard field types. For a full list, see Standard form field types.

Joomla 1.6 makes it possible to extend standard field types or define your own. For example, if your component manages phone book entries, you might want to define a form field type that outputs a select list of cities. There are several advantages to defining a custom form field type:

  • You will be able to mix standard field types with your custom field type in a JForm-based form.
  • You will eventually have a reusable code package that can be used easily throughout your code.
  • Extensions that collaborate with your extension will be able to create form fields without meddling with your database tables and other internals.

Contents

Location of files

  • The standard form field types are located in joomla/libraries/joomla/form/fields/. You should not store custom fields there, nor should you have to use this path in your own code, but the standard types are usually good examples.
  • The custom field types that belong to your component are usually located in administrator/components/<name of your component>/models/fields. You can specify this or another path in your code:
JForm::addFieldPath(JPATH_COMPONENT . DS . 'models' . DS . 'fields');
  • The XML files that define forms are usually located in administrator/components/<name of your component>/models/forms. Use something like the following snippet to specify a path to your forms:
JForm::addFormPath(JPATH_COMPONENT . DS . 'models' . DS . 'forms');

Naming conventions and skeleton

In this section, <ComponentName> represents the camel-cased name of your component and <TypeName> represents the camel-cased name of your form field type. The field's class should be placed in administrator/components/<name of your component>/models/fields/<name of your field>.php, and look like this:

<?php
// Check to ensure this file is included in Joomla!
defined('_JEXEC') or die('Restricted access');
 
jimport('joomla.form.formfield');
 
class JFormField<FieldName> extends JFormField {
 
        protected $type = '<FieldName>';
 
        public function getLabel() {
                // code that returns HTML that will be shown as the label
        }
 
        public function getInput() {
                // code that returns HTML that will be shown as the form field
        }
}

Important lines:

  • class JFormField<FieldName> extends JFormField {
    Here we create our subclass called <FieldName> and make it extend JFormField. The class name must always be the same as the filename (in camel case).
  • protected $type = '<FieldName>';
    The field class must know its own type through the variable $type. This is the same name as your class name
  • public function getLabel() {
    This function will be called to create the label that belongs to your field and must return a HTML string containing it. You do not have to define this function; if you leave it out, the standard method of creating labels will be used.
  • public function getInput() {
    This function will be called to create the field itself and must return a HTML string containing it.

Grouping custom field types

Warning: this information is partially incorrect and needs to be improved.

Custom field types can be grouped by using an underscore in the field name. A field class with a name for example like "JFormFieldMy_randomField" must be stored in administrator/components/<name of your component>/models/fields/my/randomField.php. We can prefix our form field names with some group name, then we put an underscore and then a name of a field.

Which class to subclass?

For a form field type to be usable in JForm, it needs do be a subclass of JFormField. However, it does not have to be a direct child of that class: you can also subclass an existing (standard or custom) form field type and thereby inherit useful code.

If your form field type is quite similar to an existing type, you should subclass that type. Especially if your form field type is a list, please subclass JFormFieldList. You only have to override getOptions() method to return the options to be shown; the getInput() method will convert those options to HTML.

To subclass an existing type, for example JFormFieldList, load it by adding the following to after jimport('joomla.form.formfield');:

jimport('joomla.form.helper');
JFormHelper::loadFieldClass('list');

If your form field type is unlike any existing type, subclass JFormField directly.

An example custom field type

Suppose you're working on your component named com_phonebook and you want to define a field that contains cities. Create the file administrator/components/com_phonebook/models/fields/city.php and write something similar to the following:

<?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>';
        }
}

Using the custom field type

To use the field type City, we need to update the XML file that contains the form fields. Open your XML file located in administrator/components/com_phonebook/models/forms and add the field in the usual way:

<field name="title" type="City" label="JGLOBAL_TITLE"
        description="JFIELD_TITLE_DESC"
        required="true" />

The type name is cAsE-sEnSiTiVe.

Overriding getLabel()

The getLabel() method should return a HTML string that will be used as a label for the form field. Since JFormField defines a ready-to-use getLabel() implementation, custom form field types usually do not define their own getLabel(). If you do want to create a custom label, you can still make use of the getLabel() in JFormField, for example by defining it as follows:

public function getLabel() {
     return '<span style="text-decoration: underline;">' . parent::getLabel() . '</span>';
}

This code will underline your form labels. (Please note that if your goal is to underline form labels, using CSS is the preferred way.)

If you want to do something completely different, you can of course also override it completely:

public function getLabel() {
        // Initialize variables.
        $label = '';
        $replace = '';
 
        // Get the label text from the XML element, defaulting to the element name.
        $text = $this->element['label'] ? (string) $this->element['label'] : (string) $this->element['name'];
 
        // Build the class for the label.
        $class = !empty($this->description) ? 'hasTip' : '';
        $class = $this->required == true ? $class.' required' : $class;
 
        // Add replace checkbox
        $replace = '<input type="checkbox" name="update['.$this->name.']" value="1" />';
 
        // Add the opening label tag and main attributes attributes.
        $label .= '<label id="'.$this->id.'-lbl" for="'.$this->id.'" class="'.$class.'"';
 
        // If a description is specified, use it to build a tooltip.
        if (!empty($this->description)) {
                $label .= ' title="'.htmlspecialchars(trim(JText::_($text), ':').'::' .
                                JText::_($this->description), ENT_COMPAT, 'UTF-8').'"';
        }
 
        // Add the label text and closing tag.
        $label .= '>'.$replace.JText::_($text).'</label>';
 
        return $label; 
}

This example will add a checkbox before the label.