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/*
 * Copyright 2017 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.firebase.database;

/**
 * Classes implementing this interface can be used to receive events about data changes at a
 * location. Attach the listener to a location user {@link
 * DatabaseReference#addValueEventListener(ValueEventListener)}.
 */
public interface ValueEventListener {

  /**
   * This method will be called with a snapshot of the data at this location. It will also be called
   * each time that data changes.
   *
   * @param snapshot The current data at the location
   */
  void onDataChange(DataSnapshot snapshot);

  /**
   * 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
   *
   * @param error A description of the error that occurred
   */
  void onCancelled(DatabaseError error);
}