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Flutter – Unhandled Exception: type 'String' is not a subtype of type 'Null' of 'value'

I cannot pass a null value to a key that was initially defined as null.
my host can be either String or null, but it returns the error:

[ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'String' is not a subtype of type 'Null' of 'value'

My Code:

class PreferencesBloc {
  final PreferencesRepository repository = PreferencesRepository();

  final Map<String, dynamic> _json = {
    'login': {
      'cnpj': '',
      'usuario': '',
      'senha': '',
    },
    'configuracao': {
      'host': null,
    },
  };

  void gravar() {
    _json['login']['cnpj'] = Empresa().cnpj ?? '';
    _json['login']['usuario'] = Usuario().usuario ?? '';
    _json['login']['senha'] = Usuario().senha ?? '';
    _json['configuracao']['host'] = Configuracao().host; //Error is here

    repository.whrite(_json);
  }

  Future<Map<String, dynamic>> ler() async {
    var map = await repository.read();
    map ??= _json;
    return map;
  }
}

Tem como fazer isso? Por que não está permitindo?

Tags:

2

Answers


  1. 0

    I am not sure why but this works. Hope someone explains why.

    var nullableString; 

final Map<String, dynamic> _json = {
    'login': {
      'cnpj': '',
      'usuario': '',
      'senha': '',
    },
    'configuracao': {
      'host': nullableString,
    },
  };
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  2. 0

    When you define your _json as Map<String, dynamic>, this means only first layer inside your map can accept null value, I mean you can set configuracao like this:

    final Map<String, dynamic> _json = {
    'login': {
      'cnpj': '',
      'usuario': '',
      'senha': '',
    },
    'configuracao': null, // <-- this
  };

    but , what you want is set something inside configuracao as dynamic so you need to do this:

    void gravar() {
    _json['login']['cnpj'] = Empresa().cnpj ?? '';
    _json['login']['usuario'] = Usuario().usuario ?? '';
    _json['login']['senha'] = Usuario().senha ?? '';
    Map<String, dynamic> newConfiguracao = _json['configuracao'];
    newConfiguracao['host'] = Configuracao().host;
    _json['configuracao'] = newConfiguracao;

    repository.whrite(_json);
  }
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