GF hooks

gf_pre_val_hooks.php

<?php

add_action( 'gform_pre_submission_1', 'gf_form_pre_submission' );

/**
 * Presubmission form handler
 * 
 * @hook gform_pre_submission
 */
function gf_form_pre_submission($form) {

	// iterate over the fields to obtain specific field's id
	foreach ( $form['fields'] as $field ) {

		// check if the date picker class has been added
		if ( $field['cssClass'] == 'gf-date-picker' ) {

			// get the field id
			$id = $field['id'];

			// do whatever you want with the values here (change the date format, etc.)
			$_POST['input_' . $id] = $_POST['input_' . $id];
		}
	}
}

add_filter( "gform_field_validation_1", 'gf_custom_validation', 10, 4 );

/**
 * Presubmission form handler
 * 
 * @hook gform_pre_submission
 */

/**
 * Custom GF validation function used for pagination and required fields
 *
 * @return string
 */
function gf_custom_validation($result, $value, $form, $field) {

	// lets validate only our custom field
	if ( $field['cssClass'] === 'gf-date-picker' ) {

		// let's obtain separate strings for each part of the date
		$value = array_map( 'intval', explode( '/', $value ) );
		
		// if the field is not valid then return the user
		if ( !checkdate( $value[0], $value[1], $value[2] ) ) {
			
			// add error message to the end user
			$result["is_valid"] = false;
			$result["message"] = "Wrong date, please check the format and make sure it's a valid one. ";
			
		} else {
			$result["is_valid"] = true;
		}
	}

	return $result;
}