Error with Map<String, Dynamic> - Cannot recognize String as Dynamic

Question

I have the following Flutter error:

type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String'

This error is occurring when I have run the code seginte:

  List _listaTarefas = [];
  _salvarArquivo() async{

        final diretorio = await getApplicationDocumentsDirectory();
        var arquivo =  File("${diretorio.path}/dados.json" );

        Map<String, dynamic> tarefa = Map();
        tarefa["titulo"] = "Ir ao Mercado";
        tarefa["realizada"] = false;
        _listaTarefas.add(tarefa);

        String dados = json.encode(_listaTarefas);
        arquivo.writeAsString(dados);

  }

Answer 1

Even if you have already found a solution to your problem, I will also leave here a proposal to improve your code, and maintain a clean architecture, so that it is easier for you to understand what you are writing:

If you have a task list, and the type that will be inserted in this list is always a Map<String, dynamic>, now you better set the list as:

List<Map<String, dynamic>> _listaTarefas = [];

Thus, only Map with that format can be inserted, but ok, we already understood, by the variable name, that this is a task list, but how is a task formed? What values can they have? How can I remember these values in 1 week, 1 month, without having to search for a task file to know how it is structured? Luckily, Dart is a language typified and Object-Oriented, now how about we make a class that represents a structure of a task:

class Tarefa{
  String titulo;
  bool realizada;

  Tarefa(this.titulo, this.realizada);

  Map<String, dynamic> get toMap => {
    'titulo': titulo,
    'realizada': realizada
  }

  String get toJsonString => json.encode(this.toMap);
}

And now we can change the list to:

List<Tarefa> _listaTarefas = [];

And with that your method _salvarArquivo can be simplified in this way:

_salvarArquivo() async{
  final diretorio = await getApplicationDocumentsDirectory();
  var arquivo =  File("${diretorio.path}/dados.json" );

  Tarefa tarefa = Tarefa("Ir ao Mercado", false);
  _listaTarefas.add(tarefa);
  arquivo.writeAsString(tarefa.toJsonString);
}

If you have a class with many attributes, Json Serialization can simplify your life by generating most of the conversion code between objects for you.