Errors when Adding "Show Single Variation" Code into functions.php - php

Question

In WooCommerce, I'm trying to add some custom code into my active theme's functions.php file, which will enable for variable products to display the attribute dropdowns, the quantity field and the add to cart button on shop and archive pages.
Here's my actual code:
// Display variations dropdowns on shop page for variable products
add_filter( 'woocommerce_loop_add_to_cart_link', 'woo_display_variation_dropdown_on_shop_page' );
function woo_display_variation_dropdown_on_shop_page() {
global $product;
if( $product->is_type( 'variable' )) {
$attribute_keys = array_keys( $product->get_attributes() );
?>
<form class="variations_form cart" method="post" enctype='multipart/form-data' data-product_id="<?php echo absint( $product->id ); ?>" data-product_variations="<?php echo htmlspecialchars( json_encode( $product->get_available_variations() ) ) ?>">
<?php do_action( 'woocommerce_before_variations_form' ); ?>
<?php if ( empty( $product->get_available_variations() ) && false !== $product->get_available_variations() ) : ?>
<p class="stock out-of-stock"><?php _e( 'This product is currently out of stock and unavailable.', 'woocommerce' ); ?></p>
<?php else : ?>
<table class="variations" cellspacing="0">
<tbody>
<?php foreach ( $product->get_attributes() as $attribute_name => $options ) : ?>
<tr>
<td class="label"><label for="<?php echo sanitize_title( $attribute_name ); ?>"><?php echo wc_attribute_label( $attribute_name ); ?></label></td>
<td class="value">
<?php
$selected = isset( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ? wc_clean( urldecode( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ) : $product->get_variation_default_attribute( $attribute_name );
wc_dropdown_variation_attribute_options( array( 'options' => $options, 'attribute' => $attribute_name, 'product' => $product, 'selected' => $selected ) );
echo end( $attribute_keys ) === $attribute_name ? apply_filters( 'woocommerce_reset_variations_link', '<a class="reset_variations" href="#">' . __( 'Clear', 'woocommerce' ) . '</a>' ) : '';
?>
</td>
</tr>
<?php endforeach;?>
</tbody>
</table>
<?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>
<div class="single_variation_wrap">
<?php
/**
* woocommerce_before_single_variation Hook.
*/
do_action( 'woocommerce_before_single_variation' );
/**
* woocommerce_single_variation hook. Used to output the cart button and placeholder for variation data.
* #since 2.4.0
* #hooked woocommerce_single_variation - 10 Empty div for variation data.
* #hooked woocommerce_single_variation_add_to_cart_button - 20 Qty and cart button.
*/
do_action( 'woocommerce_single_variation' );
/**
* woocommerce_after_single_variation Hook.
*/
do_action( 'woocommerce_after_single_variation' );
?>
</div>
<?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>
<?php endif; ?>
<?php do_action( 'woocommerce_after_variations_form' ); ?>
</form>
<?php } else {
echo sprintf( '<a rel="nofollow" href="%s" data-quantity="%s" data-product_id="%s" data-product_sku="%s" class="%s">%s</a>',
esc_url( $product->add_to_cart_url() ),
esc_attr( isset( $quantity ) ? $quantity : 1 ),
esc_attr( $product->id ),
esc_attr( $product->get_sku() ),
esc_attr( isset( $class ) ? $class : 'button' ),
esc_html( $product->add_to_cart_text() )
);
}
}
But the following errors are thrown and having issues making it work:
Your PHP code changes were rolled back due to an error on line 666 of file wp-content/plugins/woocommerce-composite-products/includes/wc-cp-template-functions.php. Please fix and try saving again.
Uncaught Error: Call to a member function get_type() on null in
wp-content/plugins/woocommerce-composite-products/includes/wc-cp-template-functions.php:666
Stack trace:
#0 wp-includes/class-wp-hook.php(286): wc_cp_before_add_to_cart_button('')
#1 wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array)
#2 wp-includes/plugin.php(465): WP_Hook->do_action(Array)
#3 wp-content/themes/electro-child/functions.php(2228): do_action('woocommerce_bef...')
#4 wp-includes/class-wp-hook.php(288): woo_display_variation_dropdown_on_shop_page('<a href="https:...')
#5 wp-includes/plugin.php(208): WP_Hook->apply_filters('<a href="https:...', Array)
#6 wp-content/plugins/woocommerce/templates/loop/add
I think there's a conflict with the Composite product plugin I'm using.
Any help is hugely appreciated.

Answer 1

The biggest mistake in your code is that you just forgot that you are using a filter hook and in that case, you need to return the output, but not to echo it.
Then you will use the hook arguments that are included in this filter hook instead.
Also you just need to change the behavior for variable products only, because, with your actual code, as you are also using the WooCommerce Composite Products plugin, it gives you the reported error.
So try instead something like (untested):
// Display variations dropdowns on shop page for variable products
add_filter( 'woocommerce_loop_add_to_cart_link', 'woo_display_variation_dropdown_on_shop_page', 10, 3 );
function woo_display_variation_dropdown_on_shop_page( $add_to_cart_link, $product, $args ) {
if( $product->is_type('variable') ) {
$attribute_keys = array_keys( $product->get_attributes() );
ob_start(); // Start buffering
?>
<form class="variations_form cart" method="post" enctype='multipart/form-data' data-product_id="<?php echo absint( $product->id ); ?>" data-product_variations="<?php echo htmlspecialchars( json_encode( $product->get_available_variations() ) ) ?>">
<?php do_action( 'woocommerce_before_variations_form' ); ?>
<?php if ( empty( $product->get_available_variations() ) && false !== $product->get_available_variations() ) : ?>
<p class="stock out-of-stock"><?php _e( 'This product is currently out of stock and unavailable.', 'woocommerce' ); ?></p>
<?php else : ?>
<table class="variations" cellspacing="0">
<tbody>
<?php foreach ( $product->get_attributes() as $attribute_name => $options ) : ?>
<tr>
<td class="label"><label for="<?php echo sanitize_title( $attribute_name ); ?>"><?php echo wc_attribute_label( $attribute_name ); ?></label></td>
<td class="value">
<?php
$selected = isset( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ? wc_clean( urldecode( $_REQUEST[ 'attribute_' . sanitize_title( $attribute_name ) ] ) ) : $product->get_variation_default_attribute( $attribute_name );
wc_dropdown_variation_attribute_options( array( 'options' => $options, 'attribute' => $attribute_name, 'product' => $product, 'selected' => $selected ) );
echo end( $attribute_keys ) === $attribute_name ? apply_filters( 'woocommerce_reset_variations_link', '<a class="reset_variations" href="#">' . __( 'Clear', 'woocommerce' ) . '</a>' ) : '';
?>
</td>
</tr>
<?php endforeach;?>
</tbody>
</table>
<?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>
<div class="single_variation_wrap">
<?php
/**
* woocommerce_before_single_variation Hook.
*/
do_action( 'woocommerce_before_single_variation' );
/**
* woocommerce_single_variation hook. Used to output the cart button and placeholder for variation data.
* #since 2.4.0
* #hooked woocommerce_single_variation - 10 Empty div for variation data.
* #hooked woocommerce_single_variation_add_to_cart_button - 20 Qty and cart button.
*/
do_action( 'woocommerce_single_variation' );
/**
* woocommerce_after_single_variation Hook.
*/
do_action( 'woocommerce_after_single_variation' );
?>
</div>
<?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>
<?php endif; ?>
<?php do_action( 'woocommerce_after_variations_form' ); ?>
</form>
<?php
$add_to_cart_link = ob_get_clean(); // The buffered content
}
return $add_to_cart_link;
}