Add Custom Donation Field With Dynamic Value

/**

 * This example shows how you can add a new donation field to be displayed

 * in Charitable emails related to donations.

 */

/**

 * Register the extra field.

 *

 * @param   array            $fields

 * @param   Charitable_Email $email

 * @return  array

 */

function ed_charitable_add_extra_donation_field( $fields, Charitable_Email $email ) {

	if ( ! in_array( 'donation', $email->get_object_types() ) ) {

		return $fields;

	}

	$fields['extra_donation_field'] = array(

		'description' => __( 'Extra field description', 'your-namespace' ),

		'callback'    => 'ed_charitable_get_extra_donation_field_value',

	);

	return $fields;

}

add_filter( 'charitable_email_content_fields', 'ed_charitable_add_extra_donation_field', 10, 2 );

/**

 * Get the content to be displayed for the extra donation field.

 *

 * @param   string           $default

 * @param   array            $args

 * @param   Charitable_Email $email

 * @return  string

 */

function ed_charitable_get_extra_donation_field_value( $default, $args, $email ) {

	if ( ! $email->has_valid_donation() ) {

		return '';

	}

	if ( 'yes' === get_post_meta( $email->get_donation()->ID, 'extra_donation_field', true ) ) {

		return 'some text';

	} else {

		return 'some other text';

	}

}

/**

 * To help with previewing emails, you can also define a fake value for your field.

 *

 * @param   array            $fields

 * @param   Charitable_Email $email

 * @return  array

 */

function ed_charitable_preview_extra_donation_field( $fields, Charitable_Email $email ) {

	if ( ! in_array( 'donation', $email->get_object_types() ) ) {

		return $fields;

	}

	$fields['extra_donation_field'] = 'My Fake Value';

	return $fields;

}

add_filter( 'charitable_email_preview_content_fields', 'ed_charitable_preview_extra_donation_field', 10, 2 );