Flutter - 为什么我会收到“未处理的异常：迭代期间并发修改”从数据库查询？

Question

我在理解有关颤振数据库处理的问题时遇到了一些困难（至少我这么认为，因为这就是问题所在）。当我运行我的应用程序时，我收到以下错误消息：

E/flutter (26185): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: Concurrent modification during iteration: Instance(length:13) of '_GrowableList'.
E/flutter (26185): #0      ListIterator.moveNext (dart:_internal/iterable.dart:336:7)
E/flutter (26185): #1      _MyHomePageState._processBle.<anonymous closure> (package:blescanner/screens/home_view.dart:283:27)
E/flutter (26185): <asynchronous suspension>

我花了很多精力试图找出原因。引用的第 283 行是 MyHomePage 中的“for (var element in list){”行，但据我所知，我并没有尝试在任何地方修改该列表。一段时间后，我开始逐行注释以查找问题的原因，结果发现当我注释掉“dbHelper.getBlItemLog”调用时，问题消失了。这让我进入了该函数（代码包含在下面），其中问题似乎是数据库查询。我认为这可能是查询期间修改数据库的一些问题，因此我删除了对数据库的所有其他调用，但问题仍然存在。数据库查询怎么会导致这种问题呢？我就是不明白为什么？有人对此有什么见解或建议吗？

来自 MyHomePage（扩展了 Stateful Widget）：

  void _processBle() {
    FlutterBluePlus.instance.scanResults.forEach((list) async {
      for (var element in list) {
        String bleName = element.device.name;
        dev.log('Found device: ' + bleName);
        String blItemId = bleName.replaceAll('XXX', '');
        var blItemData = CustomBluetoothItem.fromBle(bleName,
            blItemId,
            element.advertisementData.manufacturerData,
            _geoPos.lat, _geoPos.long
        );
        int tempStatus = blItemData.status;
        try {
          if (blItemData.status > 1) {
            await lock.synchronized(() async {
              dev.log('${DateTime.now()
                  .toIso8601String()} _processBle .. start $bleName');

              //here's where I call the troubling function

              await dbHelper.getBlItemLog(
                  bleName: bleName, startDate: blItemData.sDate)
                  .then((queueItem) async {
                // the stuff in here is commented away for now and thus doesn't matter
              });


              dev.log('${DateTime.now()
                  .toIso8601String()} _processBle .. stop ${element.device
                  .name}');
            });
          }
        } catch (e) {
          dev.log('error : $e');
        }
      }
    });
    firstStartup = false;
    dev.log('_processBle - ### done');
  }

来自我的 dbHelper：

  Future<CustomBluetoothItem?> getBlItemLog({required String bleName, required String startDate}) async {
    Database? db = await database;

   //the following line seems to be where the issue is, since there's no issue if I comment it away.
    
   List<Map<String, dynamic>> maps = await db!.rawQuery('SELECT * FROM ble_table WHERE bleName = ? AND startDate = ? ORDER BY createDate desc limit 1 offset 0',[bleName,startDate]);
    
    if (maps.isNotEmpty) {
      return CustomBluetoothItem.fromJson(maps[0]);
    }
    return null;
  }