+ /**
+ * Callback that is invoked when a notification listener subscribes for a
+ * particular notification type.
+ * <p>
+ * This method is only called for the first subscription that occurs for a
+ * particular notification type. Subsequent subscriptions for the same
+ * notification type do not trigger invocation of this method.
+ * <p>
+ * <b>Note:</b>This callback is delivered from thread not owned by this listener,
+ * all processing should be as fast as possible and implementations should
+ * not do any blocking calls or block this thread.
+ *
+ * @param notificationType the notification type for the subscription that occurred.
+ */