java - 类型 'List' 不是类型转换中类型 'List<>' 的子类型

Question

我想做的是在 Flutter 和 Android 之间进行通信。为此，我使用 EventChannel 和 MethodChannel。由于编解码器的限制，我需要在将 Android 数据发送到 Flutter 之前将其包装在 HashMap 中。在 Flutter 方面，我试图将其解包以显示在简单的 ListView 中。但是，我无法弄清楚的类型转换问题

factory BLEService.fromMap(Map<String, dynamic> map) => BLEService(
    map['uuid'] as String,
    (map['characteristics'] as List<BLECharacteristic>)
        .map<BLECharacteristic>((e)  =>
      BLECharacteristic.fromMap(e as Map<String, BLECharacteristic>)
    ).toList()
  );

对于这一行，将引发以下异常: type 'List<Object?>' is not a subtype of type 'List<BLECharacteristic>' in type cast帮助解决这个问题将不胜感激

编辑
Flutter BLECharacteristic.fromMap

factory BLECharacteristic.fromMap(Map<String, dynamic> map) => BLECharacteristic(
    map['uuid'] as String,
  );

Java BLECharacteristic.toMap

HashMap<String, Object> toMap() {
        HashMap<String, Object> bleCharacteristicMap = new HashMap<>();
        bleCharacteristicMap.put("uuid", uuid);
        return bleCharacteristicMap;
    }

Answer 1

在 Flutter 中，map['characteristics']将返回 List<Object?>而不是 List<BLECharacteristic> .所以下面的代码可能对你有用(未经测试):

factory BLEService.fromMap(Map<String, dynamic> map) => BLEService(
    map['uuid'] as String,
    (map['characteristics'] as List)
        ?.map((e)  =>
      BLECharacteristic.fromMap(e as Map<String, dynamic>)
    ).toList()
  );

你能显示 fromMap和 toMap BLECharactertic 的方法以便更好地理解问题。