content: /*
   * Copyright (C) 2018 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package android.util;
  
  import android.content.ContentResolver;
  import android.database.ContentObserver;
  import android.net.Uri;
  import android.os.Handler;
  
  /**
   * Abstract class for observing changes to a specified setting stored as a comma-separated key value
   * list of parameters. Registers and unregisters a {@link ContentObserver} and handles updates when
   * the setting changes.
   *
   * <p>Subclasses should pass in the relevant setting's {@link Uri} in the constructor and implement
   * {@link #update(KeyValueListParser)} to receive updates when the value changes.
   * Calls to {@link #update(KeyValueListParser)} only trigger after calling {@link
   * #start()}.
   *
   * <p>To get the most up-to-date parameter values, first call {@link #start()} before accessing the
   * values to start observing changes, and then call {@link #stop()} once finished.
   *
   * @hide
   */
  public abstract class KeyValueSettingObserver {
      private static final String TAG = "KeyValueSettingObserver";
  
      private final KeyValueListParser mParser = new KeyValueListParser(',');
  
      private final ContentObserver mObserver;
      private final ContentResolver mResolver;
      private final Uri mSettingUri;
  
      public KeyValueSettingObserver(Handler handler, ContentResolver resolver,
              Uri uri) {
          mObserver = new SettingObserver(handler);
          mResolver = resolver;
          mSettingUri = uri;
      }
  
      /** Starts observing changes for the setting. Pair with {@link #stop()}. */
      public void start() {
          mResolver.registerContentObserver(mSettingUri, false, mObserver);
          setParserValue();
          update(mParser);
      }
  
      /** Stops observing changes for the setting. */
      public void stop() {
          mResolver.unregisterContentObserver(mObserver);
      }
  
      /**
       * Returns the {@link String} representation of the setting. Subclasses should implement this
       * for their setting.
       */
      public abstract String getSettingValue(ContentResolver resolver);
  
      /** Updates the parser with the current setting value. */
      private void setParserValue() {
          String setting = getSettingValue(mResolver);
          try {
              mParser.setString(setting);
          } catch (IllegalArgumentException e) {
              Slog.e(TAG, "Malformed setting: " + setting);
          }
      }
  
      /** Subclasses should implement this to update references to their parameters. */
      public abstract void update(KeyValueListParser parser);
  
      private class SettingObserver extends ContentObserver {
          private SettingObserver(Handler handler) {
              super(handler);
          }
  
          @Override
          public void onChange(boolean selfChange) {
              setParserValue();
              update(mParser);
          }
      }
  }
  