1 /* 2 * Copyright (C) 2007 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.database; 18 19 import java.util.ArrayList; 20 21 /** 22 * Provides methods for registering or unregistering arbitrary observers in an {@link ArrayList}. 23 * 24 * This abstract class is intended to be subclassed and specialized to maintain 25 * a registry of observers of specific types and dispatch notifications to them. 26 * 27 * @param T The observer type. 28 */ 29 public abstract class Observable<T> { 30 /** 31 * The list of observers. An observer can be in the list at most 32 * once and will never be null. 33 */ 34 protected final ArrayList<T> mObservers = new ArrayList<T>(); 35 36 /** 37 * Adds an observer to the list. The observer cannot be null and it must not already 38 * be registered. 39 * @param observer the observer to register 40 * @throws IllegalArgumentException the observer is null 41 * @throws IllegalStateException the observer is already registered 42 */ registerObserver(T observer)43 public void registerObserver(T observer) { 44 if (observer == null) { 45 throw new IllegalArgumentException("The observer is null."); 46 } 47 synchronized(mObservers) { 48 if (mObservers.contains(observer)) { 49 throw new IllegalStateException("Observer " + observer + " is already registered."); 50 } 51 mObservers.add(observer); 52 } 53 } 54 55 /** 56 * Removes a previously registered observer. The observer must not be null and it 57 * must already have been registered. 58 * @param observer the observer to unregister 59 * @throws IllegalArgumentException the observer is null 60 * @throws IllegalStateException the observer is not yet registered 61 */ unregisterObserver(T observer)62 public void unregisterObserver(T observer) { 63 if (observer == null) { 64 throw new IllegalArgumentException("The observer is null."); 65 } 66 synchronized(mObservers) { 67 int index = mObservers.indexOf(observer); 68 if (index == -1) { 69 throw new IllegalStateException("Observer " + observer + " was not registered."); 70 } 71 mObservers.remove(index); 72 } 73 } 74 75 /** 76 * Remove all registered observers. 77 */ unregisterAll()78 public void unregisterAll() { 79 synchronized(mObservers) { 80 mObservers.clear(); 81 } 82 } 83 } 84