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 (un)registering arbitrary observers in an ArrayList. 23 */ 24 public abstract class Observable<T> { 25 /** 26 * The list of observers. An observer can be in the list at most 27 * once and will never be null. 28 */ 29 protected final ArrayList<T> mObservers = new ArrayList<T>(); 30 31 /** 32 * Adds an observer to the list. The observer cannot be null and it must not already 33 * be registered. 34 * @param observer the observer to register 35 * @throws IllegalArgumentException the observer is null 36 * @throws IllegalStateException the observer is already registered 37 */ 38 public void registerObserver(T observer) { 39 if (observer == null) { 40 throw new IllegalArgumentException("The observer is null."); 41 } 42 synchronized(mObservers) { 43 if (mObservers.contains(observer)) { 44 throw new IllegalStateException("Observer " + observer + " is already registered."); 45 } 46 mObservers.add(observer); 47 } 48 } 49 50 /** 51 * Removes a previously registered observer. The observer must not be null and it 52 * must already have been registered. 53 * @param observer the observer to unregister 54 * @throws IllegalArgumentException the observer is null 55 * @throws IllegalStateException the observer is not yet registered 56 */ 57 public void unregisterObserver(T observer) { 58 if (observer == null) { 59 throw new IllegalArgumentException("The observer is null."); 60 } 61 synchronized(mObservers) { 62 int index = mObservers.indexOf(observer); 63 if (index == -1) { 64 throw new IllegalStateException("Observer " + observer + " was not registered."); 65 } 66 mObservers.remove(index); 67 } 68 } 69 70 /** 71 * Remove all registered observer 72 */ 73 public void unregisterAll() { 74 synchronized(mObservers) { 75 mObservers.clear(); 76 } 77 } 78 } 79
