<?php
/**
* Display the actual Widget
*
* @param Array $args
* @param Array $instance
*/
public function widget($args, $instance){
…
$wcss = apply_filters( 'my-filter-name', $wcss );
…
}
?>
To create your own filter hook just use the function “apply_filters” then
as you mentioned add a function in your constructor i.e.
function __constructor()
{
…
add_filter( 'my-filter-name', array( &$this, 'my_function_name' );
…
}
Be sure your function returns something
function my_function_name( $css )
{
// Do whatever you want
return $css;
}