1/*
2 * Copyright (C) 2018 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.util;
18
19import android.content.ContentResolver;
20import android.database.ContentObserver;
21import android.net.Uri;
22import android.os.Handler;
23
24/**
25 * Abstract class for observing changes to a specified setting stored as a comma-separated key value
26 * list of parameters. Registers and unregisters a {@link ContentObserver} and handles updates when
27 * the setting changes.
28 *
29 * <p>Subclasses should pass in the relevant setting's {@link Uri} in the constructor and implement
30 * {@link #update(KeyValueListParser)} to receive updates when the value changes.
31 * Calls to {@link #update(KeyValueListParser)} only trigger after calling {@link
32 * #start()}.
33 *
34 * <p>To get the most up-to-date parameter values, first call {@link #start()} before accessing the
35 * values to start observing changes, and then call {@link #stop()} once finished.
36 *
37 * @hide
38 */
39public abstract class KeyValueSettingObserver {
40    private static final String TAG = "KeyValueSettingObserver";
41
42    private final KeyValueListParser mParser = new KeyValueListParser(',');
43
44    private final ContentObserver mObserver;
45    private final ContentResolver mResolver;
46    private final Uri mSettingUri;
47
48    public KeyValueSettingObserver(Handler handler, ContentResolver resolver,
49            Uri uri) {
50        mObserver = new SettingObserver(handler);
51        mResolver = resolver;
52        mSettingUri = uri;
53    }
54
55    /** Starts observing changes for the setting. Pair with {@link #stop()}. */
56    public void start() {
57        mResolver.registerContentObserver(mSettingUri, false, mObserver);
58        setParserValue();
59        update(mParser);
60    }
61
62    /** Stops observing changes for the setting. */
63    public void stop() {
64        mResolver.unregisterContentObserver(mObserver);
65    }
66
67    /**
68     * Returns the {@link String} representation of the setting. Subclasses should implement this
69     * for their setting.
70     */
71    public abstract String getSettingValue(ContentResolver resolver);
72
73    /** Updates the parser with the current setting value. */
74    private void setParserValue() {
75        String setting = getSettingValue(mResolver);
76        try {
77            mParser.setString(setting);
78        } catch (IllegalArgumentException e) {
79            Slog.e(TAG, "Malformed setting: " + setting);
80        }
81    }
82
83    /** Subclasses should implement this to update references to their parameters. */
84    public abstract void update(KeyValueListParser parser);
85
86    private class SettingObserver extends ContentObserver {
87        private SettingObserver(Handler handler) {
88            super(handler);
89        }
90
91        @Override
92        public void onChange(boolean selfChange) {
93            setParserValue();
94            update(mParser);
95        }
96    }
97}
98