Set cart item price from a hidden input field custom price in Woocommerce 3

Question

In Woocommerce, I used jQuery to calculate a custom price on a single product pages, and now need to pass this value to the cart.

The desired behavior is

Answer 1

First for testing purpose we add a price in the hidden input field as you don't give the code that calculate the price:

// Add a hidden input field (With a value of 20 for testing purpose)
add_action( 'woocommerce_before_add_to_cart_button', 'custom_hidden_product_field', 11 );
function custom_hidden_product_field() {
    echo '<input type="hidden" id="hidden_field" name="custom_price" class="custom_price" value="20">'; // Price is 20 for testing
}

Then you will use the following to change the cart item price (WC_Session is not needed):

// Save custom calculated price as custom cart item data
add_filter( 'woocommerce_add_cart_item_data', 'save_custom_fields_data_to_cart', 10, 2 );
function save_custom_fields_data_to_cart( $cart_item_data, $product_id ) {

    if( isset( $_POST['custom_price'] ) && ! empty( $_POST['custom_price'] )  ) {
        // Set the custom data in the cart item
        $cart_item_data['custom_price'] = (float) sanitize_text_field( $_POST['custom_price'] );

        // Make each item as a unique separated cart item
        $cart_item_data['unique_key'] = md5( microtime().rand() );
    }
    return $cart_item_data;
}

// Updating cart item price
add_action( 'woocommerce_before_calculate_totals', 'change_cart_item_price', 30, 1 );
function change_cart_item_price( $cart ) {
    if ( ( is_admin() && ! defined( 'DOING_AJAX' ) ) )
        return;

    if ( did_action( 'woocommerce_before_calculate_totals' ) >= 2 )
        return;

    // Loop through cart items
    foreach ( $cart->get_cart() as $cart_item ) {
        // Set the new price
        if( isset($cart_item['custom_price']) ){
            $cart_item['data']->set_price($cart_item['custom_price']);
        }
    }
}

Code goes in function.php file of your active child theme (or active theme). Tested and works.

Related: Woocommerce set_quantity crashes site when adding products to cart