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