Observable.java revision 722fe711207a37783dfa7142284b0ebe5bd503fb 
1/*
2 * Copyright (C) 2014 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.databinding;
18
19/**
20 * Observable classes provide a way in which data bound UI can be notified of changes.
21 * {@link ObservableList} and {@link ObservableMap} also provide the ability to notify when
22 * changes occur. ObservableField, ObservableBoolean, ObservableByte, ObservableShort,
23 * ObservableInt, ObservableLong, ObservableFloat, and ObservableDouble provide
24 * a means by which properties may be notified without implementing Observable.
25 * <p>
26 * An Observable object should notify the {@link OnPropertyChangedCallback} whenever
27 * an observed property of the class changes.
28 * <p>
29 * The getter for an observable property should be annotated with {@link Bindable}.
30 * <p>
31 * Convenience class BaseObservable implements this interface and PropertyChangeRegistry
32 * can help classes that don't extend BaseObservable to implement the listener registry.
33 */
34public interface Observable {
35
36    /**
37     * Adds a callback to listen for changes to the Observable.
38     * @param callback The callback to start listening.
39     */
40    void addOnPropertyChangedCallback(OnPropertyChangedCallback callback);
41
42    /**
43     * Removes a callback from those listening for changes.
44     * @param callback The callback that should stop listening.
45     */
46    void removeOnPropertyChangedCallback(OnPropertyChangedCallback callback);
47
48    /**
49     * The callback that is called by Observable when an observable property has changed.
50     */
51    abstract class OnPropertyChangedCallback {
52
53        /**
54         * Called by an Observable whenever an observable property changes.
55         * @param sender The Observable that is changing.
56         * @param propertyId The BR identifier of the property that has changed. The getter
57         *                   for this property should be annotated with {@link Bindable}.
58         */
59        public abstract void onPropertyChanged(Observable sender, int propertyId);
60    }
61}
62