Add product selection widget to custom attribute in Magento - php

Question

Does anyone know how can I add a custom product attribute with a widget renderer?
You can see this in Promo rules if you select SKU you'll got an Ajax popup with product selection.
so how would I go about it?
in :
$installer->addAttribute(Mage_Catalog_Model_Product::ENTITY...
In other words, how can I use a widget to select custom attribute values?
EDIT:
The scenario is as follows:
I would like to create a product attribute that will, upon a button click, open a product selection widget.
After the selection, the selected SKU's will go in in a comma delimited format.
This behavior can be seen in the catalog and shopping cart price rules.
If you filter the rule by SKU (SKU attribute must be enabled to "apply to rules"), you'll get a field and a button that will open the product selection widget.

Answer 1

Here is some thoughts that should get you going on the right track:
First, in a setup script, create your entity:
$installer->addAttribute('catalog_product', 'frontend_display', array(
'label' => 'Display Test',
'type' => 'varchar',
'frontend_model' => 'Test_Module/Entity_Attribute_Frontend_CsvExport',
'input' => 'select',
'required' => 0,
'user_defined' => false,
'group' => 'General'
));
Make sure to set the frontend_model to the model that you are going to use. The frontend model affects the display of the attribute (both in the frontend and the adminhtml sections).
Next, create yourself the class, and override one or both of the following functions:
public function getInputType()
{
return parent::getInputType();
}
public function getInputRendererClass()
{
return "Test_Module_Block_Adminhtml_Entity_Renderer_CsvExport";
}
The first (getInputType()) is used to change the input type to a baked in input type (see Varien_Data_Form_Element_* for the options). However, to set your own renderer class, use the latter function - getInputRendererClass(). That is what I am going to demonstrate below:
public function getElementHtml()
{
return Mage::app()->getLayout()->createBlock('Test_Module/Adminhtml_ExportCsv', 'export')->toHtml();
}
Here, to clean things up, I am instantiating another block, as the element itself doesn't have the extra functions to display buttons and the like.
Then finally, create this file:
class Test_Module_Block_Adminhtml_ExportCsv extends Mage_Adminhtml_Block_Widget
{
protected function _prepareLayout()
{
$button = $this->getLayout()->createBlock('adminhtml/widget_button')
->setData(array(
'label' => $this->__('Generate CSV'),
'onclick' => '',
'class' => 'ajax',
));
$this->setChild('generate', $button);
}
protected function _toHtml()
{
return $this->getChildHtml();
}
}
This doesn't cover the AJAX part, but will get you very close to getting the rest to work.