Asynchronous notifications from the recording and writing of AppStats events. The application can implement this interface, and register it with the AppStatistics object, using the addAppThresholdListener method. The thresholdReached listener method will be called every time a multiple of the threshold size is reached. The threshold size for RAM and file storage can be set using the setRamSizeThreshold and setFileSizeThreshold methods. These threshold sizes apply only to memory and/or file storage consumed by AppStats events.