Magento: get a list of attribute values - list

Question

I am new to Magento and I'm building a bookshop. I have an attribute called author, and I would like to show a list of all authors (a list of their attribute values). I tried to create a widget and use this code in it but it returns me an empty array. How can I achieve this? Where should I place the code, in a widget, a block?
protected function _toHtml()
{
$name='author';
$attributeInfo = Mage::getResourceModel('eav/entity_attribute_collection')->setCodeFilter($name)->getFirstItem();
$attributeId = $attributeInfo->getAttributeId();
$attribute = Mage::getModel('catalog/resource_eav_attribute')->load($attributeId);
$attributeOptions = $attributeInfo->getSource()->getAllOptions(false);
$html = '<ul>';
foreach($attributeOptions as $opt)
$html .= '<li>'.$opt[0].'</li>';
$html .= '</ul>';
return $html;
}

Answer 1

$attributes = $product->getAttributes();
foreach ($attributes as $attribute) {
if ($attribute->getIsVisibleOnFront()) {
$value = $attribute->getFrontend()->getValue($product);
echo $value
}
}
you can get attribute with this code just write this code in view.phtml

Answer 2

Thank you very much, your code worked quite good for a particular product, however i finally get what I wanted using this:
$attributeCode='author';
// build and filter the product collection
$products = Mage::getResourceModel('catalog/product_collection')
->addAttributeToFilter($attributeCode, array('notnull' => true))
->addAttributeToFilter($attributeCode, array('neq' => ''))
->addAttributeToSelect($attributeCode);
// get all distinct attribute values
$usedAttributeValues = array_unique($products->getColumnValues($attributeCode));
sort($usedAttributeValues);