How to take a certain data index of Future item

Question

I Have a problem to take the newest data index

class User {
  final String idUser,
  name,
  phone;

  User(
    {this.idUser,
    this.name,
    this.phone});

  factory User.fromJson(Map<String, dynamic> json) {
    return User(
    idUser: json['_id'],
    name: json['name'],
    phone: json['phone']);
  }
}

List<User> userFromJson(jsonData) {
  List<User> result =
    List<User>.from(jsonData.map((item) => User.fromJson(item)));

  return result;
}

// index
Future<List<User>> fetchUser() async {
  String route = AppConfig.API_ENDPOINT + "userdata";
  final response = await http.get(route);
  if (response.statusCode == 200) {
    var jsonResp = json.decode(response.body);

    return userFromJson(jsonResp);
  } else {
    throw Exception('Failed load $route, status : ${response.statusCode}');
  }
}

and the calling method just like this

user = fetchUser();

the "response.body" valued like this

[{"_id":"4136425eb8d9320f4822c554","name":"John","phone":"90643755394"},{"_id":"62766b2eb45s3w0g4662ftd3","name":"Anna","timestamp":"90345765791"}]

I expect it was how to take the first index to get the newest data, but I don't know ho the code will be. Also if there are another soltion to get that newest data, please let me know, thank you very much

Ananda Pramono · Answer 1 · 2021-12-15T01:14:48.067

1

You can use array index number to get the first object in array.

 if (response.statusCode == 200) {
    var jsonResp = json.decode(response.body);

    return List<User>.from(jsonResp.map((user) => User.fromJson(user)));
  } else {
    throw Exception('Failed load $route, status : ${response.statusCode}');
  }

If you want to get one user only

 if (response.statusCode == 200) {
    var jsonResp = json.decode(response.body);

    return User.fromJson(jsonResp[0]);
  } else {
    throw Exception('Failed load $route, status : ${response.statusCode}');
  }

Other method is by modifying the Query using LIMIT 1

edited Dec 15 '21 at 01:14

answered Dec 10 '21 at 06:46

Ananda Pramono

899
1
6
18

on the List userFromJson(jsondata) it return error _TypeError (type '(dynamic) => User' is not a subtype of type '(String, dynamic) => MapEntry' of 'transform') – Alfan Dec 10 '21 at 07:02
can you post your json result? So we have a clear image about how to handle the data – Ananda Pramono Dec 10 '21 at 16:19
the response.body valued: [{"_id":"4136425eb8d9320f4822c554","name":"John","phone":"90643755394"},{"_id":"62766b2eb45s3w0g4662ftd3","name":"Anna","timestamp":"90345765791"}] – Alfan Dec 14 '21 at 09:52
Okay I edit my answer, please check it. – Ananda Pramono Dec 15 '21 at 01:12
using User.fromJson(jsonResp[0]); returning error on me A value of type 'User' can't be returned from the function 'fetchUser' because it has a return type of 'Future>'.dartreturn_of_invalid_type – Alfan Dec 15 '21 at 02:27
how about the method of "Other method is by modifying the Query using LIMIT 1"? – Alfan Dec 15 '21 at 02:34
@Alfan for that error, change `Future>` to `Future`. The other method is change your query, so something like this `SELECT * FROM user LIMIT 1`. – Ananda Pramono Dec 15 '21 at 02:44
I don't know it represent succesful or not, when I print the variable into string, it valued Instance of 'User' – Alfan Dec 15 '21 at 06:37
Yup, because you access the user directly, try user.name – Ananda Pramono Dec 15 '21 at 06:38

score 1 · Accepted Answer · answered Dec 10 '21 at 06:48

1

Use index to get the specific value from a list

userFromJson(jsonResp[0]); /// For first record

answered Dec 10 '21 at 06:48

s.am.i

648
5
16

on the List userFromJson(jsondata) it return error _TypeError (type '(dynamic) => User' is not a subtype of type '(String, dynamic) => MapEntry' of 'transform') – Alfan Dec 10 '21 at 07:02
Okay keep everything as yours and return result[0] – s.am.i Dec 10 '21 at 07:07
it's turn out invalid syntax A value of type 'User' can't be returned from the function 'userFromJson' because it has a return type of 'List'. – Alfan Dec 10 '21 at 07:21
Is the total list returning from above code – s.am.i Dec 10 '21 at 07:25
I mean if I modify return result into return result[0] the word "result[0]" underlined red, so it could not be run – Alfan Dec 10 '21 at 09:12
Without doing any changes will your code return the list??? – s.am.i Dec 10 '21 at 09:13
yes it return a list – Alfan Dec 10 '21 at 09:40
Okay then get user[0] – s.am.i Dec 10 '21 at 10:07
it works on my program, thank you very much – Alfan Dec 19 '21 at 06:28

score 0 · Answer 3 · answered Dec 10 '21 at 08:24

0

Because its Future You have to use the await keyword to get the completed result so modify your code by adding await

users = await fetchUser();

now you can access the user list

var firstUser = users.first;
var firstUser = users[0];

For more await and async you can read this Asynchronous programming

answered Dec 10 '21 at 08:24

Mutasim

36
5

is "users.first" mean the attribute named "first" in a class named "user" of object name "users"? – Alfan Dec 10 '21 at 09:15
no its attribute of the List users[0] and users.first give the same result – Mutasim Dec 10 '21 at 09:41
https://api.dart.dev/stable/2.15.0/dart-core/List/first.html – Mutasim Dec 10 '21 at 09:58
if I print the firstUser, it valued Instance of 'User' – Alfan Dec 15 '21 at 06:35
Your data its a List and firstUser its the first element from that list so you can access the `firstUser.idUser` and `firstUser.name` and `firstUser.phone` – Mutasim Dec 15 '21 at 07:19

How to take a certain data index of Future item

3 Answers3