Magento configuration - populating field when using frontend_model - configuration

Question

I have specified a frontend_model in system.xml for an entry field. I did this because I wanted to make a field read-only. There may have been a more straightforward way to achieve that, but that's where I am at the moment. The thing is I cannot get the field to display the data it should.
I have a button that when pressed, populates the read-only field. That works fine. But when I hit 'Save Config', the data disappears from the field. The reason it disappears is because I can't find out what I should set the field's value to. Below tries using the getEscapedValue() method of Varien_Data_Form_Element_Abstract, but it returns nothing. And as usual with Magento, there is no documentation to speak of.
class Mypackage_MyModule_Block_Adminhtml_System_Config_DisabledText extends Mage_Adminhtml_Block_System_Config_Form_Field
{
protected function _prepareLayout()
{
parent::_prepareLayout();
if (!$this->getTemplate()) {
$this->setTemplate('mypackage/system/config/disabled_text.phtml');
}
return $this;
}
public function render(Varien_Data_Form_Element_Abstract $element)
{
$element->unsScope()->unsCanUseWebsiteValue()->unsCanUseDefaultValue();
return parent::render($element);
}
protected function _getElementHtml(Varien_Data_Form_Element_Abstract $element)
{
$originalData = $element->getOriginalData();
$this->addData(array(
'my_value' => $element->getEscapedValue(),
'html_id' => $element->getHtmlId(),
));
return $this->_toHtml();
}
}
disabled_text.phtml contains the following:
<input id="<?php echo $this->getHtmlId() ?>" value="<?php echo $this->getMyValue(); ?>" class=" input-text" type="text" disabled/>
Thanks.

Answer 1

This is one of those places where you need to look at how Magento itself is doing something similar to what you want to do. If you look at the Mage_Adminhtml_Block_System_Config_Form_Field class's _getElementHtml
protected function _getElementHtml(Varien_Data_Form_Element_Abstract $element)
{
return $element->getElementHtml();
}
you can see that this method accepts a form element that's already been instantiated (based on what's in system.xml), and then this element renders itself with getElementHtml. That means when Magento needs to render (and, in turn, get the value) it does so in from the element object. Some crude debugging will let us know where getElementHtml can be located
protected function _getElementHtml(Varien_Data_Form_Element_Abstract $element)
{
var_dump(get_class($element));
return $element->getElementHtml();
}
Something like Varien_Data_Form_Element_Text will be dumped to the screen. In turn, this class inherits form Varien_Data_Form_Element_Abstract, which contains the following definition
public function getElementHtml()
{
$html = '<input id="'.$this->getHtmlId().'" name="'.$this->getName()
.'" value="'.$this->getEscapedValue().'" '.$this->serialize($this->getHtmlAttributes()).'/>'."\n";
$html.= $this->getAfterElementHtml();
return $html;
}
So, when Magento wants to get the value for a system config field, it uses the above PHP code to render the input. So, if you want to do the same in your template, I'd try something like this
Up in the class, assign a block property with the entire element. This is actually more efficient that plucking values out of the elements, since all PHP needs to store is an object reference.
protected function _getElementHtml(Varien_Data_Form_Element_Abstract $element)
{
$this->setMyElement($element);
return $this->_toHtml();
}
Then, in the template, copy the code from magento's rendering, replacing the "$this" keyword with your saved element
<?php $_element = $this->getMyElement(); ?>
<!-- check the quoting/escaping on this html/php, I didn't actually run it, but the concept is sound -->
<input disabled="disabled" id="<?php echo $_element->getHtmlId();?>" name="<?php echo $_element->getName();?>"
value="<?php echo $_element->getEscapedValue();?>"
<?php echo $_element->serialize($_element->getHtmlAttributes());?>
/>
<?php echo $_element->getAfterElementHtml(); ?>
When you're working with Magento, try to think like a Magento developer. Instead of "I need to figure out how to make it do X", think "I need to add this feature to the store in the same way the rest of my teammates have". Then look how the core team did it, and copy their implementation, changing as little as you need to.
It does get easier the more you work with the system!