Gravity Forms - dynamically populate fields

functions.php

<?php
/* *** replace "your_parameter" with the parameter in the advanced tab 
https://docs.gravityforms.com/using-dynamic-population/  */

add_filter( 'gform_field_value_your_parameter', 'my_custom_population_function' );
function my_custom_population_function( $value ) {
    return 'boom!';
}

/*Use this for a real estate form */
add_filter( 'gform_field_value_property_name', 'wap_populate_post_title' );
function wap_populate_post_title( $value ) {
	// bail if we aren't on a single listing CPT
	if ( ! is_singular( 'listing' ) ) {
		return;
	}
	// fetch the post title
	$title = get_the_title();
	// return value escaped
	return esc_html( $title );
}