SettingsProvider之onCreate、lookupValue、call

转载请注明出处：http://blog.csdn.net/droyon/article/details/35558735

一、onCreate

• 构建USER_OWNER的Databases以及相关缓冲数据表。
  establishDbTracking(UserHandle.USER_OWNER);
• 构建广播监听。
  
  getContext().registerReceiver(new BroadcastReceiver() {
              @Override
              public void onReceive(Context context, Intent intent) {
                  if (intent.getAction().equals(Intent.ACTION_USER_REMOVED)) {
                      final int userHandle = intent.getIntExtra(Intent.EXTRA_USER_HANDLE,
                              UserHandle.USER_OWNER);
                      if (userHandle != UserHandle.USER_OWNER) {
                          onUserRemoved(userHandle);
                      }
                  }
              }
          }, userFilter);

二、lookupValue

• 读取缓冲。
  Bundle value = cache.get(key);
              if (value != null) {
                  if (value != TOO_LARGE_TO_CACHE_MARKER) {
                      return value;
                  }
                  // else we fall through and read the value from disk
              } else if (cache.fullyMatchesDisk()) {//当前已经全部和Disk（硬盘）保持了一直，没有必要读去硬盘。
                  // Fast path (very common).  Don't even try touch disk
                  // if we know we've slurped it all in.  Trying to
                  // touch the disk would mean waiting for yaffs2 to
                  // give us access, which could takes hundreds of
                  // milliseconds.  And we're very likely being called
                  // from somebody's UI thread...
                  //不要试图读取硬盘，假如我们知道我们已经读取了所有的数据。
                  return NULL_SETTING;
              }
  
• 从数据库 中读取数据
  
  1、try {
              cursor = db.query(table, COLUMN_VALUE, "name=?", new String[]{key},
                                null, null, null, null);
              if (cursor != null && cursor.getCount() == 1) {
                  cursor.moveToFirst();
                  return cache.putIfAbsent(key, cursor.getString(0));//更新cache并返回
              }
          }
  2、加入cursor.getCount == 1，那么：cache.putIfAbsent方法：
  public Bundle putIfAbsent(String key, String value) {
              Bundle bundle = (value == null) ? NULL_SETTING : Bundle.forPair("value", value);
              if (value == null || value.length() <= MAX_CACHE_ENTRY_SIZE) {//如果value为null，或者value的长度小于500字符
                  synchronized (this) {
                      if (get(key) == null) {
                          put(key, bundle);//bundle可能：NULL_SETTINGS、Bundle.forPair("value", value)
                      }
                  }
              }//【value不为null，且value的长度大于500，直接返回bundle，bundle为Bundle.forPair("value", value)】
              return bundle;
          }
  3、如果上一步出现一场，或者cursor==null，那么就要跳出这一层，然后执行：cache.putIfAbsent(key, null)
  cache.putIfAbsent(key, null);
  更新cache的内容为NULL_SETTINGS。
  
  

三、call的方法执行。

• 根据不同GET_方法，执行lookupValue方法。
  if (Settings.CALL_METHOD_GET_SYSTEM.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call(system:" + request + ") for " + callingUser);
              dbHelper = getOrEstablishDatabase(callingUser);
              cache = sSystemCaches.get(callingUser);
              return lookupValue(dbHelper, TABLE_SYSTEM, cache, request);
          }
          if (Settings.CALL_METHOD_GET_SECURE.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call(secure:" + request + ") for " + callingUser);
              dbHelper = getOrEstablishDatabase(callingUser);
              cache = sSecureCaches.get(callingUser);
              return lookupValue(dbHelper, TABLE_SECURE, cache, request);
          }
          if (Settings.CALL_METHOD_GET_GLOBAL.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call(global:" + request + ") for " + callingUser);
              // fast path: owner db & cache are immutable after onCreate() so we need not
              // guard on the attempt to look them up
              return lookupValue(getOrEstablishDatabase(UserHandle.USER_OWNER), TABLE_GLOBAL,
                      sGlobalCache, request);
          }
  
• 根据不同PUT_方法，执行insertForUser。
  final ContentValues values = new ContentValues();
          values.put(Settings.NameValueTable.NAME, request);
          values.put(Settings.NameValueTable.VALUE, newValue);
          if (Settings.CALL_METHOD_PUT_SYSTEM.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call_put(system:" + request + "=" + newValue + ") for " + callingUser);
              insertForUser(Settings.System.CONTENT_URI, values, callingUser);
          } else if (Settings.CALL_METHOD_PUT_SECURE.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call_put(secure:" + request + "=" + newValue + ") for " + callingUser);
              insertForUser(Settings.Secure.CONTENT_URI, values, callingUser);
          } else if (Settings.CALL_METHOD_PUT_GLOBAL.equals(method)) {
              if (LOCAL_LOGV) Slog.v(TAG, "call_put(global:" + request + "=" + newValue + ") for " + callingUser);
              insertForUser(Settings.Global.CONTENT_URI, values, callingUser);
          } else {
              Slog.w(TAG, "call() with invalid method: " + method);
          }