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      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 
     17 package android.util;
     18 
     19 import android.content.ContentResolver;
     20 import android.database.ContentObserver;
     21 import android.net.Uri;
     22 import 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  */
     39 public 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