How to display all product attribute in my custom grid

Question

How to display all product attribute in my custom grid i am using the below code but its returning results in array format can you please correct me where i am doing wrong

 $this->addColumn('action',
            array(
                'header'    =>  Mage::helper('kems')->__('Magento Attribute'),
                'width'     => '100',
                'align'     => 'center',
                'type'      => 'select',
                'getter'    => 'getId',
                'renderer'  => 'Kensium_Kems_Block_Adminhtml_Renderer_Attribute',
                'filter'    => false,
                'sortable'  => false,
                'index'     => 'magento_attribute',
                'is_system' => true,
            ));

===================================================

public function render(Varien_Object $row)
    {

    $url ='';
    $html =array();

    $attributes = Mage::getResourceModel('catalog/product_attribute_collection')
                                        ->getItems();

    foreach ($attributes as $attribute){

     $html[] = $attribute->getFrontendLabel();

    }

   //echo '<pre>';
   print_r($html);
    //die;
    return array_keys($html);
}

Answer 1

here i can give you concept to make drop down in grid not your full solution

you can return array like this with help of below function

 public function toOptionArray()
    {
$columns = array(
    array(
        'value' => 'id',   
        'label' => __('ID')
    ),

);

$columnsCollection = 
    Mage::getResourceModel('eav/entity_attribute_collection')
    ->setEntityTypeFilter( Mage::getModel('eav/entity')->setType('catalog_product')->getTypeId() )
->addFilter("is_visible", 1);

foreach($columnsCollection->getItems() as $column) 
{
    $columns[] = array(
        'value' => $column->getAttributeCode(),   
        'label' => $column->getFrontendLabel()
    );
}

    return $columns;
}

EDIT For select box

instead of using renderer you can also use select box in grid like below

$columnsCollection = 
        Mage::getResourceModel('eav/entity_attribute_collection')
        ->setEntityTypeFilter( Mage::getModel('eav/entity')->setType('catalog_product')->getTypeId() )
    ->addFilter("is_visible", 1);

    foreach($columnsCollection->getItems() as $column) 
    {
        $columns[$column->getAttributeCode()] =  $column->getFrontendLabel();
    }


  $this->addColumn('your_attribute', array(
            'header' => Mage::helper('modulename')->__('Your attribute'),
            'index' => 'your_attribute',
            'type' => 'options',
            'options'=> $columns;
            ));

But as i seen in your question you are going to add Action.. Dont know why you have to add this attribute dropdown in action