Custom filter in the sales order admin grid giving php strict notice error

Question

I've been able to add columns to the sales order grid table in admin, but when I try to use the column to search I get an error Strict Notice: call_user_func() expects parameter 1 to be a valid callback, non-static method filterSkus() should not be called statically

Here's the observer function

public function filterSkus($collection, $column)
{
    if (!$value = $column->getFilter()->getValue()) {
        return $this;
    }

    $collection->getSelect()->having(
        "group_concat(`m_sales_flat_order_item`.sku SEPARATOR ', ') like ?", "%$value%");

    return $this;
}

Here's the data helper calling it

public function getSkusColumnParams()
{
    return array(
        'header' => 'SKUs',
        'index' => 'skus',
        'type' => 'text',
        'filter_condition_callback' => array('DR_Salesgridder_Model_Observer', 'filterSkus'),
    );
}

The stack error is coming from call_user_func in Mage/Adminhtml/Block/Widget/Grid.php

protected function _addColumnFilterToCollection($column)
{
    if ($this->getCollection()) {
        $field = ( $column->getFilterIndex() ) ? $column->getFilterIndex() : $column->getIndex();
        if ($column->getFilterConditionCallback()) {
            call_user_func($column->getFilterConditionCallback(), $this->getCollection(), $column);
        }

I made the filterSkus function static, but it gives me the error undefined variable: this. Beyond removing the strict reporting, is there another way?

Answer 1

Use the observer instance, replacing

array('DR_Salesgridder_Model_Observer', 'filterSkus'),

with

array(Mage::getSingleton('salesgridder/observer'), 'filterSkus'),

(you might need to change the class alias "salesgridder/observer" based on your configuration