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
17package android.database;
18
19import 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 */
29public 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     */
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     */
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     */
78    public void unregisterAll() {
79        synchronized(mObservers) {
80            mObservers.clear();
81        }
82    }
83}
84