Snippet to populate Gravity Forms checkbox field with values from custom post type

gf-populate-checkboxes.php

<?php

// Replace 8 with your form ID
add_filter( 'gform_pre_render_8', 'populate_activity_field' );
add_filter( 'gform_pre_validation_8', 'populate_activity_field' );
add_filter( 'gform_pre_submission_filter_8', 'populate_activity_field' );
add_filter( 'gform_admin_pre_render_8', 'populate_activity_field' );

function populate_activity_field( $form ) {
	foreach ( $form['fields'] as &$field ) {
		if ( strpos( $field->cssClass, 'activities' ) === false ) { // Replace 'activities' with your field class name
			continue;
		}

		$choices = array();
		$activities = get_posts( 'numberposts=-1&post_type=activity' ); // Replace with your custom post type
		$field_id = $field->id;
		$input_id = 1;

		foreach ( $activities as $activity ) {
			if ( $input_id % 10 == 0 ) {
					$input_id++;
			}

			$choices[] = array( 'text' => html_entity_decode($activity->post_title), 'value' => html_entity_decode($activity->post_title) );
			
			// Labels with post image
			// $thumbnail = wp_get_attachment_image_src( get_post_thumbnail_id($activity->ID), 'thumbnail' );
			// $choices[] = array( 'text' => '<img src="' . $thumbnail[0] . '"><span>' . html_entity_decode($activity->post_title) . '</span>', 'value' => html_entity_decode($activity->post_title) );
			
			$inputs[] = array( 'label' => html_entity_decode($activity->post_title), 'id' => "{$field_id}.{$input_id}" );
			$input_id++;
		}

	$field->choices = $choices;
	$field->inputs = $inputs;

	break;
	}
	return $form;
}

?>