WP_Widget::update_callback

	public function update_callback( $deprecated = 1 ) {
		global $wp_registered_widgets;

		$all_instances = $this->get_settings();

		// We need to update the data.
		if ( $this->updated ) {
			return;
		}

		if ( isset( $_POST['delete_widget'] ) && $_POST['delete_widget'] ) {
			// Delete the settings for this instance of the widget.
			if ( isset( $_POST['the-widget-id'] ) ) {
				$del_id = $_POST['the-widget-id'];
			} else {
				return;
			}

			if ( isset( $wp_registered_widgets[ $del_id ]['params'][0]['number'] ) ) {
				$number = $wp_registered_widgets[ $del_id ]['params'][0]['number'];

				if ( $this->id_base . '-' . $number == $del_id ) {
					unset( $all_instances[ $number ] );
				}
			}
		} else {
			if ( isset( $_POST[ 'widget-' . $this->id_base ] ) && is_array( $_POST[ 'widget-' . $this->id_base ] ) ) {
				$settings = $_POST[ 'widget-' . $this->id_base ];
			} elseif ( isset( $_POST['id_base'] ) && $_POST['id_base'] == $this->id_base ) {
				$num      = $_POST['multi_number'] ? (int) $_POST['multi_number'] : (int) $_POST['widget_number'];
				$settings = array( $num => array() );
			} else {
				return;
			}

			foreach ( $settings as $number => $new_instance ) {
				$new_instance = stripslashes_deep( $new_instance );
				$this->_set( $number );

				$old_instance = isset( $all_instances[ $number ] ) ? $all_instances[ $number ] : array();

				$was_cache_addition_suspended = wp_suspend_cache_addition();
				if ( $this->is_preview() && ! $was_cache_addition_suspended ) {
					wp_suspend_cache_addition( true );
				}

				$instance = $this->update( $new_instance, $old_instance );

				if ( $this->is_preview() ) {
					wp_suspend_cache_addition( $was_cache_addition_suspended );
				}

				/**
				 * Filters a widget's settings before saving.
				 *
				 * Returning false will effectively short-circuit the widget's ability
				 * to update settings.
				 *
				 * @since 2.8.0
				 *
				 * @param array     $instance     The current widget instance's settings.
				 * @param array     $new_instance Array of new widget settings.
				 * @param array     $old_instance Array of old widget settings.
				 * @param WP_Widget $this         The current widget instance.
				 */
				$instance = apply_filters( 'widget_update_callback', $instance, $new_instance, $old_instance, $this );
				if ( false !== $instance ) {
					$all_instances[ $number ] = $instance;
				}

				break; // Run only once.
			}
		}

		$this->save_settings( $all_instances );
		$this->updated = true;
	}