位置参数太多：预期为 0，但发现有 6 个颤振

Question

我有一个 user model class 如下所示

class User {
  String? email;
  String? about;
  String? name;
  String? picture;
  int? index;
  String? imageFetchType;

  User({this.email, this.about, this.name, this.picture, this.index, this.imageFetchType});

  factory User.fromJson(Map<String, dynamic> json) => User(
    email: json["email"],
    about: json["about"],
    name: json["name"],
    picture: json["picture"],
    index: json["index"],
    imageFetchType: json["imageFetchType"]
  );

  Map<String, dynamic> toJson() => {
    "email": email,
    "about": about,
    "name": name,
    "picture": picture,
    "index": index,
    "imageFetchType": imageFetchType
  };
}

下面是一个 Future function，我用它来获取用户 list 并循环遍历列表以填充用户

 Future<List<User>> _fetchUsersListUsingLoop() async {
    try {
     
      var response = await http.get(
          Uri.parse(
              "https://api.json-generator.com/templates/Eh5AlPjYVv6C/data"),
          headers: {
            "Content-Type": "application/json",
            "Authorization": "Bearer tltsp6dmnbif01jy9xfo9ssn4620u89xhuwcm5t3",
          });


      List<User> usersList = [];

      for (var u in json.decode(response.body)) {
        User user = User(u["email"], u["about"], u["name"], u["picture"],
            u["index"], u["imageFetchType"]);

        usersList.add(user);
      }

      return usersList;
    } catch (e) {
      log("FetchUsersListUsingLoopException $e");

      rethrow;
    }
  }

我在下一行Too many positional arguments: 0 expected, but 6 found. (Documentation) Try removing the extra positional arguments, or specifying the name for named arguments.

User user = User(u["email"], u["about"], u["name"], u["picture"],
            u["index"], u["imageFetchType"]);

当我尝试将 user class 中的 constructor 更改为低于其工作时


User(this.email, this.about, this.name, this.picture, this.index, this.imageFetchType);

但我在 fromJson 中收到另一个错误，在下面的代码行中显示 6 positional argument(s) expected, but 0 found. (Documentation) Try adding the missing arguments.

factory User.fromJson(Map<String, dynamic> json) => User(
    email: json["email"],
    about: json["about"],
    name: json["name"],
    picture: json["picture"],
    index: json["index"],
    imageFetchType: json["imageFetchType"]
  );

我怎样才能在用户 class 中使用构造函数 User({this.email, this.about, this.name, this.picture, this.index, this.imageFetchType}); 并在不出现 Too many positional arguments: 0 expected, but 6 found 错误的情况下循环

Answer 1

if server response is jsonArray, after jsonDecoding jsonArrary. you have to convert your model(List of model) by using map..

 Future<List<User>> _fetchUsersListUsingLoop() async {
try {
  var response = await http.get(
      Uri.parse(
          "https://api.json-generator.com/templates/Eh5AlPjYVv6C/data"),
      headers: {
        "Content-Type": "application/json",
        "Authorization": "Bearer tltsp6dmnbif01jy9xfo9ssn4620u89xhuwcm5t3",
      });


  List jsonResponse = json.decode(response.body);
 List<User> usersList =  jsonResponse.map((data) =>User.fromJson(data)).toList();
         print(usersList );
  return usersList;
} catch (e) {
  log("FetchUsersListUsingLoopException $e");

  rethrow;
}
  }

位置参数太多：预期为 0，但发现有 6 个颤振

Too many positional arguments: 0 expected, but 6 found flutter

constructor

arguments

for-loop

dart

flutter