Adding a Custom Form Element to an Adminhtml Form

Is there a way to add a custom form element to a Magento Adminhtml form without placing the custom element in the lib/Varian folder?

I've tracked down the code that's essentially a Varian_Data_Form_Element_ factory

public function addField($elementId, $type, $config, $after=false)
{
    if (isset($this->_types[$type])) {
        $className = $this->_types[$type];
    }
    else {
        $className = 'Varien_Data_Form_Element_'.ucfirst(strtolower($type));
    }
    $element = new $className($config);
    $element->setId($elementId);
    if ($element->getRequired()) {
        $element->addClass('required-entry');
    }
    $this->addElement($element, $after);
    return $element;
}

So, if I'm reading this correctly, I ensure that an EAV attribute's frontend returns a specific fieldType, (such as supertextfield) and the system will instantiate/render a Varien_Data_Form_Element_Supertextfield when displaying this attribute's editing form.

This is well and good, but it means I need to include my custom form element in the lib/Varian folder hierarchy. Given how module oriented Magento is, it seems like this is doing it wrong.

I realize I could jank around with a custo autoloader or symlinks in the lib, but I'm primarily interested in learning if there's

A canonical way to add custom form elements for attributes
A canonical way to customize the Magento autoloader.

This is an old post but it still can be usefull for someone :

yes you can.

The code below is located in : app/code/local/MyCompany/MyModule/Block/MyForm.php

class MyCompany_MyModule_Block_MyForm extends Mage_Adminhtml_Block_Widget_Form 
{       
    protected function _prepareForm()
    {
        $form = new Varien_Data_Form(array(
            'id'        => 'edit_form',
            'action'    => $this->getUrl('*/*/save'),
            'method'    => 'post'
        ));

        $fieldset = $form->addFieldset('my_fieldset', array('legend' => 'Your fieldset title')));

        //Here is what is interesting us          
        //We add a new type, our type, to the fieldset
        //We call it extended_label
        $fieldset->addType('extended_label','MyCompany_MyModule_Lib_Varien_Data_Form_Element_ExtendedLabel');

        $fieldset->addField('mycustom_element', 'extended_label', array(
            'label'         => 'My Custom Element Label',
            'name'          => 'mycustom_element',
            'required'      => false,
            'value'     => $this->getLastEventLabel($lastEvent),
            'bold'      =>  true,
            'label_style'   =>  'font-weight: bold;color:red;',
        ));
    }
}

Here is the code of your custom element, which is located in app/code/local/MyCompany/MyModule/Lib/Varien/Data/Form/Element/ExtendedLabel.php :

class MyCompany_MyModule_Lib_Varien_Data_Form_Element_ExtendedLabel extends Varien_Data_Form_Element_Abstract
{
    public function __construct($attributes=array())
    {
        parent::__construct($attributes);
        $this->setType('label');
    }

    public function getElementHtml()
    {
        $html = $this->getBold() ? '<strong>' : '';
        $html.= $this->getEscapedValue();
        $html.= $this->getBold() ? '</strong>' : '';
        $html.= $this->getAfterElementHtml();
        return $html;
    }

    public function getLabelHtml($idSuffix = ''){
        if (!is_null($this->getLabel())) {
            $html = '<label for="'.$this->getHtmlId() . $idSuffix . '" style="'.$this->getLabelStyle().'">'.$this->getLabel()
                . ( $this->getRequired() ? ' <span class="required">*</span>' : '' ).'</label>'."\n";
        }
        else {
            $html = '';
        }
        return $html;
    }
}

The class Varien_Data_Form_Abstract has a method addType() where you can add new element types and their respective class names. To exploit this functionality you can copy the block Mage_Adminhtml_Block_Widget_Form to the local code pool and extend the method _getAdditionalElementTypes():

protected function _getAdditionalElementTypes()
{
    $types = array(
        'my_type' => 'Namespace_MyModule_Block_Widget_Form_Element_MyType',
    );

    return $types;
}

As the class Mage_Adminhtml_Block_Widget_Form is a base class for all the other form classes, unfortunately just rewriting the block in the config will not work.

EDIT: If you need the custom element types in just one form you could override the specific class and add the type there by overriding the method _getAdditionelElementTypes(). This would be a cleaner solution than copying an importend magento class to the local code pool.

EDIT2: Looking at Mage_Adminhtml_Block_Widget_Form::_setFieldset() there is another possibility: If the attribute has a value in frontend_input_renderer (e.g. mymodule/element_mytype) then a block with that name is loaded. See also Mage/Eav/Model/Entity/Attribute/Frontend/Abstract.php line 160. This should work without overriding any Magento classes.

Self help desk strikes again. It looks like Magento sets up include paths in such a way that you can drop class files from lib (not just from the Mage_ namespace) in your local code branch

app/code/local/Varien/etc

When the autoloader tries to load a lib/Varien class, it will check your directory first. This still puts you at risk if Varien ever creates a data element with the same name as yours, but as risks go it's relatively low.

来源：https://stackoverflow.com/questions/1993597/adding-a-custom-form-element-to-an-adminhtml-form

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