Having trouble extracting JSON data from an API in a Flutter application

Question

Having trouble extracting JSON data from an API in a Flutter application

My goal is to retrieve and parse JSON data from a REST API in node.js using express and MongoDB, and then present it as userdata. However, no matter what I attempt, I am unable to successfully parse the data. It either throws an exception like "Unhandled Exception: NoSuchMethodError: Class '_InternalLinkedHashMap' has no instance method 'cast' with matching arguments," or it simply displays null. The JSON data that I am trying to parse looks like this:

{"userData":{"_id":"5d3c29fdb1b0fd22182ae683","personName":"Damian","userIdentificationEMAIL":"[email protected]","dateofbirth":"14.07.2000","grad":"Los Angeles","postanskibroj":"2B","ulica":"Jackovina","drzava":"California","faiID":"123456789","nacionalniID":"000"},"request":{"type":"GET","url":"http://localhost:3000/products"}}

The "request" field in the JSON data is not actually necessary for anything - some have suggested that it is falsely referenced. Additionally, if helpful, I can place the entire "userData" in an array when fetched from the API.

I have attempted to use Quicktype without success, along with various examples and methods found on Stack Overflow and other sources. Unfortunately, none of these approaches have yielded positive results.

Although I am able to obtain the data from the API, I am struggling to properly parse it and subsequently display the user's information.

In essence, my objective is to successfully parse the data, display it in a list or text format, store it in a variable, and utilize it throughout the application. Any assistance would be greatly appreciated. Thank you and cheers!

json flutter

Answer 1

Answer №1

By making the necessary changes to the JSON text and converting it into a JSON array, your code will function correctly.

To enhance the elegance of your code, consider modifying the factory constructor as shown below:

  factory UserData.fromJson(Map<String, dynamic> json) => UserData(
        userData: json["userData"]
            .map<UserDatum>((x) => UserDatum.fromJson(x))
            .toList(),
        request: Request.fromJson(json["request"]),
      );

You can access fields like this:

  print(UserData.fromJson(decode).userData[0].dateofbirth);

Answer 2

By making the necessary changes to the JSON text and converting it into a JSON array, your code will function correctly.

To enhance the elegance of your code, consider modifying the factory constructor as shown below:

  factory UserData.fromJson(Map<String, dynamic> json) => UserData(
        userData: json["userData"]
            .map<UserDatum>((x) => UserDatum.fromJson(x))
            .toList(),
        request: Request.fromJson(json["request"]),
      );

You can access fields like this:

  print(UserData.fromJson(decode).userData[0].dateofbirth);

Answer 3

Answer №2

There seems to be a syntax error in your json data.

I have analyzed the data you provided with the question.

To assist you, try generating dart code for your classes by visiting this link

You will receive an Autogenerated Class initially followed by its sub classes.

UPDATE

Since you have updated the question and posted error-free json code, I have made slight changes to the answer

If you decide to rename the Autogenerated class, ensure to also update it in the method below

Then proceed to pass your json data to the function as shown

fetchData() async{
  Response response;
  response = await get("yourURL");
  var json = jsonDecode(response.body);
  List<Autogenerated> _userDataList = Autogenerated.fromJson(json); 
}

Answer 4

There seems to be a syntax error in your json data.

I have analyzed the data you provided with the question.

To assist you, try generating dart code for your classes by visiting this link

You will receive an Autogenerated Class initially followed by its sub classes.

UPDATE

Since you have updated the question and posted error-free json code, I have made slight changes to the answer

If you decide to rename the Autogenerated class, ensure to also update it in the method below

Then proceed to pass your json data to the function as shown

fetchData() async{
  Response response;
  response = await get("yourURL");
  var json = jsonDecode(response.body);
  List<Autogenerated> _userDataList = Autogenerated.fromJson(json); 
}

Having trouble extracting JSON data from an API in a Flutter application

Answer №1

Answer №2

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