public enum Importance
Default notification importance: shows everywhere, makes noise, but does not visually intrude.
Higher notification importance: shows everywhere, makes noise and peeks. May use full screen intents.
Low notification importance: shows everywhere, but is not intrusive.
Min notification importance: only shows in the shade, below the fold. This should not be used with Service.startForeground since a foreground service is supposed to be something the user cares about so it does not make semantic sense to mark its notification as minimum importance. If you do this as of Android version O the system will show a higher-priority notification about your app running in the background.
A notification with no importance: does not show in the shade.
Value signifying that the user has not expressed an importance. This value is for persisting preferences, and should never be associated with an actual notification.