get_post_value example

$this->start_capturing_option_updates();
        $parsed_id   = $this->parse_widget_id( $widget_id );
        $option_name = 'widget_' . $parsed_id['id_base'];

        /* * If a previously-sanitized instance is provided, populate the input vars * with its values so that the widget update callback will read this instance */
        $added_input_vars = array();
        if ( ! empty( $_POST['sanitized_widget_setting'] ) ) {
            $sanitized_widget_setting = json_decode( $this->get_post_value( 'sanitized_widget_setting' ), true );
            if ( false === $sanitized_widget_setting ) {
                $this->stop_capturing_option_updates();
                return new WP_Error( 'widget_setting_malformed' );
            }

            $instance = $this->sanitize_widget_instance( $sanitized_widget_setting, $parsed_id['id_base'] );
            if ( is_null( $instance ) ) {
                $this->stop_capturing_option_updates();
                return new WP_Error( 'widget_setting_unsanitized' );
            }