Registers a
DataTreeChangeListener to receive
notifications when data changes under a given path in the conceptual data
tree.
You are able to register for notifications for any node or subtree
which can be represented using
DataTreeIdentifier.
You are able to register for data change notifications for a subtree or leaf
even if it does not exist. You will receive notification once that node is
created.
If there is any pre-existing data in the data tree for the path for which you are
registering, you will receive an initial data change event, which will
contain all pre-existing data, marked as created.
This method returns a
ListenerRegistration object. To
"unregister" your listener for changes call the
ListenerRegistration#close()method on the returned object.
You MUST explicitly unregister your listener when you no longer want to receive
notifications. This is especially true in OSGi environments, where failure to
do so during bundle shutdown can lead to stale listeners being still registered.