IMPORTANT: In July 2025, we stopped releasing new versions of KTX modules, and we removed the KTX libraries from the Firebase Android BoM (v34.0.0). If you use KTX APIs from the previously released KTX modules, we recommend that you migrate your app to use KTX APIs from the main modules instead. For details, see the FAQ about this initiative.

ValueEventListener

interface ValueEventListener

Classes implementing this interface can be used to receive events about data changes at a location. Attach the listener to a location user addValueEventListener.

Summary

Public functions
`Unit`	`onCancelled(error: DatabaseError)` This method will be triggered in the event that this listener either failed at the server, or is removed as a result of the security and Firebase Database rules.
`Unit`	`onDataChange(snapshot: DataSnapshot)` This method will be called with a snapshot of the data at this location.

Public functions

onCancelled

fun onCancelled(error: DatabaseError): Unit

This method will be triggered in the event that this listener either failed at the server, or is removed as a result of the security and Firebase Database rules. For more information on securing your data, see: Security Quickstart

Parameters
`error: DatabaseError`	A description of the error that occurred

onDataChange

fun onDataChange(snapshot: DataSnapshot): Unit

This method will be called with a snapshot of the data at this location. It will also be called each time that data changes.

Parameters
`snapshot: DataSnapshot`	The current data at the location