未处理的异常：键入“列表”<dynamic> ' 不是类型 'Map 的子类型<dynamic, dynamic> ' --Flutter - 实时数据库 -</dynamic,></dynamic>

Question

I am trying to get the information of the latest added to the database. I have seen on the internet that one way to get the information is this,

await _lastKeyRef.once().then((DataSnapshot snapshot) {
  if (snapshot.value != null) {
    Map<dynamic, dynamic> _values = snapshot.value;
    _values.forEach((key, value) { 
       .... code ...
    });
 { 
{ 

but it gives me an error.

I leave the code to see if someone can help me.

Picture of Realtime Database structure

final String _uid = SupermarketApp.sharedPreferences.getString(SupermarketApp.userUID);
final _turnRef = FirebaseDatabase.instance
      .reference()
      .child('cod')
      .child('service');


Future<void> createTurn() async {
    var _lastKeyRef = _turnRef.orderByKey().limitToLast(1);
    DateTime _timeNow = new DateTime.now();
    int _lastNumber;
    int _setNumber;

    await _lastKeyRef.once().then((DataSnapshot snapshot) {
      if (snapshot.value != null) {
        Map<dynamic, dynamic> _values = snapshot.value;
        _values.forEach((key, value) {
          _lastNumber = int.parse(key) + 1;
          _setNumber = value['num'] + 1;
        });

        if (_setNumber > 99) _setNumber = 1;

        _turnRef.child(_lastNumber.toString()).set(
            {'app': true, 'user_id': _uid, 'date': _timeNow.toString(), 'num': _setNumber});
      } else {
        _turnRef
            .child('1')
            .set({'app': true, 'user_id': _uid, 'date': _timeNow.toString(), 'num': 1});
      }
    });
}

Picture of the error

Thank you.

--Edit--

The code is good. The Exeption was due to having a "1" as a key in realtime database. I dont know why, but i change the key name and it works.

Answer 1

The error is because snapshot.value returns a List but you're reading it as a Map .

Updating the code to the one below should fix this:

    List<dynamic> _values = snapshot.value;
    _values.forEach((element) {
    int key = _values.indexOf(element)l
    _lastNumber = int.parse(key) + 1;
    _setNumber = element['num'] + 1;
    });