Creating a custom form field type
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.
Form field type class requirements
A form field type is defined in a
class that must be a (not necessarily direct) subclass of JFormField. To work correctly, the class must define at least two methods:
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. Since JFormField
defines a ready-to-use
getLabel() implementation, custom form field types usually do not define their own getLabel(). If you leave it out, the inherited method of creating labels will be used. It is recommended to leave out the getLabel() method for consistency and speed unless you actually want to modify the label's HTML.
public function getInput()
- This function will be called to create the field itself and must
return a HTML string containing it. This is also where most of the
processing usually happens. In our phone book City field example, this
function will have to retrieve a list of available cities and return a
HTML
<select> with the cities inserted as <option>s.
Inside your code, you will have to process the attributes set by the
field's user in the XML form definition. Some of those attributes are
accessible via protected member variables of JFormField. For example,
the
name attribute is available in your code as
$this->name. Similarly,
label,
description,
default,
multiple and
class are also available as properties of
$this. Other parameters you might have defined can be accessed through the
$this->element array: the attribute
size will be in
$this->element['size'].
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.
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 . '/models/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 . '/models/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');
// The class name must always be the same as the filename (in camel case)
class JFormField<FieldName> extends JFormField {
//The field class must know its own type through the variable $type.
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
}
}
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.
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.
In addition, you may need to add the field path to the parent <fieldset>:
<fieldset addfieldpath="/administrator/components/<component name>/models/fields">
Overriding getLabel()
As mentioned in the section
Form field type class requirements, 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() that every field type class inherits from 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.
