Dart - Parse Nested Json Arrays

Question

Getting errors after trying to convert nested JSON data using dart's factory concept. Here I have two classes to handle the json data, but still getting this error:

Exception has occurred. _TypeError (type 'FormatException' is not a subtype of type 'Map')

Here is the code:


    class BodyResponse {
      final Map<String, dynamic> message;
      BodyResponse({
        this.message
      });
      factory BodyResponse.fromJson(Map<String, dynamic> json) {
        return BodyResponse(message: json['message']);
      }
    }

    class ErrorResponse {
      final BodyResponse body;
      final int status;
      final String contentType;
      final bool success;

      ErrorResponse({
        this.body, this.status, this.contentType, this.success
      });

      factory ErrorResponse.fromJson(Map<String, dynamic> json) {
        return ErrorResponse(
          body: BodyResponse.fromJson(json['body']),
          status: json['status'],
          contentType: json['content_type'],
          success: json['success']
        );
      }
    }

    ErrorResponse errors = ErrorResponse.fromJson("""
      {
        "body": {
          "message": "Some one has already taken this username(fooBar), please try again with a new username."
        },
        "status": 500,
        "content_type": "application\/json",
        "success": false
      }
    """);

    print(errors);

What could go wrong here?

The value you pass as an argument at ErrorResponse errors = ErrorResponse.fromJson(...) seems to be a string, while the function expects it to be a map (Map<String, dynamic> json). — Egor
– Egor, Commented Jun 8, 2019 at 12:22

Egor · Accepted Answer · 2019-06-08 12:58:34Z

1

Modified most of your code here. Hope that this is what you tried to achieve.

import 'dart:convert';

class BodyResponse {
  final String message;
  BodyResponse({this.message});

  BodyResponse.fromJson(Map<String, dynamic> json):
    message = json['message'];

  factory BodyResponse.fromString(String encodedJson) {
    return BodyResponse.fromJson(json.decode(encodedJson));
  }

  Map<String, dynamic> toJson() => {
    "message": message,
  };

  String toString() => json.encode(this.toJson());

}

class ErrorResponse {
  final BodyResponse body;
  final int status;
  final String contentType;
  final bool success;

  ErrorResponse({this.body, this.status, this.contentType, this.success});

  ErrorResponse.fromJson(Map<String, dynamic> json):
    body = BodyResponse.fromJson(json['body']),
    status = json['status'],
    contentType = json['content_type'],
    success = json['success'];

  factory ErrorResponse.fromString(String encodedJson) {
    return ErrorResponse.fromJson(json.decode(encodedJson));
  }

  Map<String, dynamic> toJson() => {
    "body": body.toJson(),
    "status": status,
    "contentType": contentType,
    "success": success,
  };

  String toString() => json.encode(this.toJson());

}

void main() {
  ErrorResponse errors = ErrorResponse.fromString("""
      {
        "body": {
          "message": "Some one has already taken this username(fooBar), please try again with a new username."
        },
        "status": 500,
        "content_type": "application\/json",
        "success": false
      }
    """);
  print(errors);
}

Let me know if this helped.

answered Jun 8, 2019 at 12:58

Egor

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6 Comments

rakibtg Over a year ago

You solution works just fine when i run it in a dart environment. But when i am trying to use this inside a catch block again it seems to break :( Here is a screenshot: i.sstatic.net/WnOUe.png

rakibtg Over a year ago

I've tried with both ErrorResponse.fromJson and ErrorResponse.fromString method

rakibtg Over a year ago

Also, the JSON somehow getting an extra { at the end of the string! i.sstatic.net/rcp9G.png

Egor Over a year ago

@rakibtg you are trying to get the server error response from local Dart exception (e). I believe you should use the same response.body with fromString method instead.

rakibtg Over a year ago

Thanks George for your time. From my JS knowledge i was trying with this try...catch block: i.imgur.com/07BUPdg.png Do you think according to dart it is possible? :)

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