Wordpress apply_filters() Arguments Missing

Question

I'm customizing a Woocommerce Wordpress site.

In the Woocommerce product class (class-wc-product.php) the get_price function applies a filter as follows:

function get_price() {
    return apply_filters('woocommerce_get_price', $this->price, $this);
}

In my functions.php I want to add a filter as follows:

add_filter('woocommerce_get_price', 'custom_price');

function custom_price($price, $product) {
    ...
}

When I call this I get the following PHP warning:

Warning: Missing argument 2 for custom_price()

Why is the second argument missing? Is $this not sent to the filter call?

Answer 1

It's missing the second argument because you didn't tell WordPress you wanted it with your add_filter call. By default, actions and filters only get one argument. Try this:

<?php
add_filter('woocommerce_get_price', 'custom_price', 10, 2);

function custom_price($price, $product) {
    ...
}

Answer 2

The warning is a result of the second argument in your function custom_price(). The filter provides only one variable on the call and I can't remember if this is the product/post ID or the price. The code docs indicate that it returns a string so I'd presume it's the price.

You can hopefully find the documentation at http://wcdocs.woothemes.com/apidocs/index.html

If you need the product at this point you'll have to use:

function custom_price( $price ) {

    global $product;

}

If all else fails simply echo $price to see if you can tell if it's a product ID or a price. Then adjust your code accordingly.