addChangeListener abstract method
Adds a listener to be notified of changes to the results of this query.
A new listener will be called with the current results, after being added. Subsequently it will only be called when the results change, either because the contents of the database have changed or this query's parameters have been changed through setParameters.
Adding a listener
If a Future is returned, the listener will only start listening after the Future has completed. Otherwise the listener is listening immediately after this method returns.
Removing a listener
The returned ListenerToken needs to be provided to
removeChangeListener, to remove the given listener. Regardless of
whether a Future is returned or not, the listener immediately stops
being called.
See also:
- QueryChange for the change event given to
listener. - removeChangeListener for removing a previously added listener.
Implementation
FutureOr<ListenerToken> addChangeListener(QueryChangeListener listener);