Can't convert Map to List in Dart, facing "Unhandled Exception: type 'List<dynamic-CodePudding

I know this question has been asked, but I'll explain my problem and show you what I've tried.

So, I receive a response from an API, that looks exactly like this:

[
    {
        "id": 1,
        "nome": "Macarrão",
        "descricao": "Macarrão Parafuso 100g",
        "preco": 10.23,
        "imagem": "https://www.-------.com.br/ccstore/v1/images/?source=/file/v3396941523676425853/products/141618_0.jpg"
    },
    {
        "id": 2,
        "nome": "Nescau",
        "descricao": "Achocolatado Nescau",
        "preco": 5.23,
        "imagem": "https://www.-------.com.br/ccstore/v1/images/?source=/file/v3396941523676425853/products/141618_0.jpg"
    },
    {
        "id": 3,
        "nome": "Toddynho",
        "descricao": "Bedida láctea - Toddynho",
        "preco": 2.48,
        "imagem": "https://www.-------.com.br/ccstore/v1/images/?source=/file/v3396941523676425853/products/141618_0.jpg"
    },
    {
        "id": 4,
        "nome": "Toddynho",
        "descricao": "Bedida láctea - Toddynho",
        "preco": 2.48,
        "imagem": "https://www.-----.com.br/ccstore/v1/images/?source=/file/v3396941523676425853/products/141618_0.jpg"
    }
]

Those are products that have 5 attributes, and I want to display them(the products) on screen. Right now my code looks like this:

Future<void> loadProducts() async {
    final response = await http.get(Uri.parse(_url));
    if (response.body == null) return;
    Map<String, dynamic> data = jsonDecode(response.body);
    print(response.body);
    data.forEach((productId, productData) {
      _items.add(
        Product(
          id: productId,
          nome: productData['nome'],
          descricao: productData['descricao'],
          preco: productData['preco'],
          imagem: productData['imagem'],
        ),
      );
    });

    notifyListeners();
  }

Product is

class Product with ChangeNotifier {
  final String id;
  final String nome;
  final String descricao;
  final double preco;
  final String imagem;
  bool isFavorite;

  Product({
    required this.id,
    required this.nome,
    required this.descricao,
    required this.preco,
    required this.imagem,
    this.isFavorite = false,
  });

  void toggleFavorite() {
    isFavorite = !isFavorite;
    notifyListeners();
  }
}

and I have tried solutions like this:

List<String> respApi =
        (jsonDecode(response.body) as List<dynamic>).cast<String>();

from this answer , or this one

var usersDataFromJson = parsedJson['data'];
List<String> userData = List<String>.from(usersDataFromJson);

that would result in the error The argument type 'void Function(String, dynamic)' can't be assigned to the parameter type 'void Function(String)'.

Thanks again for your help.

CodePudding user response：

If you look at your json, you see it's a List of Map, but on this line

Map<String, dynamic> data = jsonDecode(response.body);

you are putting it inside a Map so it's logic to get an error. So, to resolve the error, do this

List<Map> data  = jsonDecode(response.body); //or List<Map<String, dynamic>> data = ...

but if it throws TypeError, do this instead

List data = jsonDecode(response.body);

And you can access your data like this

for(var element in data) {
   element.forEach((k,v) {
      //operations
   }) ;
}

CodePudding user response：

I think you get the error on the line _items.add. So based on te code in my previous answer it should be like this

_items.add( 
   Product(
      id: element['id'] ,
      nome: element['nome'],
      descricao: element['descricao'],
      preco: element['preco'],
      imagem: element['imagem'],
    )
)

and you don't need to use forEach anymore. Also for your Product class I advice you declare id of type int instead of String to avoid errors since in your json id is an int.