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 @android.ravenwood.annotation.RavenwoodKeepWholeClass
30 public abstract class Observable<T> {
31     /**
32      * The list of observers.  An observer can be in the list at most
33      * once and will never be null.
34      */
35     protected final ArrayList<T> mObservers = new ArrayList<T>();
36 
37     /**
38      * Adds an observer to the list. The observer cannot be null and it must not already
39      * be registered.
40      * @param observer the observer to register
41      * @throws IllegalArgumentException the observer is null
42      * @throws IllegalStateException the observer is already registered
43      */
registerObserver(T observer)44     public void registerObserver(T observer) {
45         if (observer == null) {
46             throw new IllegalArgumentException("The observer is null.");
47         }
48         synchronized(mObservers) {
49             if (mObservers.contains(observer)) {
50                 throw new IllegalStateException("Observer " + observer + " is already registered.");
51             }
52             mObservers.add(observer);
53         }
54     }
55 
56     /**
57      * Removes a previously registered observer. The observer must not be null and it
58      * must already have been registered.
59      * @param observer the observer to unregister
60      * @throws IllegalArgumentException the observer is null
61      * @throws IllegalStateException the observer is not yet registered
62      */
unregisterObserver(T observer)63     public void unregisterObserver(T observer) {
64         if (observer == null) {
65             throw new IllegalArgumentException("The observer is null.");
66         }
67         synchronized(mObservers) {
68             int index = mObservers.indexOf(observer);
69             if (index == -1) {
70                 throw new IllegalStateException("Observer " + observer + " was not registered.");
71             }
72             mObservers.remove(index);
73         }
74     }
75 
76     /**
77      * Remove all registered observers.
78      */
unregisterAll()79     public void unregisterAll() {
80         synchronized(mObservers) {
81             mObservers.clear();
82         }
83     }
84 }
85