Parsing JSON in Dart

Question

I'm trying to parse JSON to an object in Dart, the documentation uses Map type to parse a JSON response.

regarding to their documentation Using Dart with JSON Web Services: Parsing JSON ,I snipped the following example:

import 'dart:convert';

main() {
  String mapAsJson = '{"language":"dart"}';  // input Map of data
  Map parsedMap = JSON.decode(mapAsJson);
  print(parsedMap["language"]); // dart
}

I applied the same in my testApp, however it didn't work

test() {
  var url = "http://localhost/wptest/wp-json/wp/v2/posts";

  // call the web server asynchronously
  var request = HttpRequest.getString(url).then(onDataLoaded);
}

onDataLoaded(String responseText) {
  Map x = JSON.decode(responseText);
  print(x['title'].toString());
}

I'm getting this error

Exception: Uncaught Error: type 'List' is not a subtype of type 'Map' of 'x'.
Stack Trace:
  post.post (package:untitled8/wp/posts.dart:25:24)
  onDataLoaded (http://localhost:63342/untitled8/web/index.dart:24:15)
  _RootZone.runUnary (dart:async/zone.dart:1166)
  _Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:494)
  _Future._propagateToListeners (dart:async/future_impl.dart:577)
  _Future._completeWithValue (dart:async/future_impl.dart:368)
  _Future._asyncComplete.<anonymous closure> (dart:async/future_impl.dart:422)
  _microtaskLoop (dart:async/schedule_microtask.dart:43)
  _microtaskLoopEntry (dart:async/schedule_microtask.dart:52)
  _ScheduleImmediateHelper._handleMutation (dart:html:42567)

@stevenupton yes the error was because my JSON was a list. I will post the answer in minutes. — Murhaf Sousli
– Murhaf Sousli, Commented Nov 7, 2015 at 11:35

Teddie · Accepted Answer · 2022-07-25 09:57:35Z

2

The JSON coming from the sever need to be decoded to a json in dart and assigned to a map of type String and dynamic

The keys in the json have to String while their value pair has to be of type dynamic in other to hold any value be it an array or int or bool

  Map<String,dynamic> z = Map<String,dynamic>.from(JSON.decode(responseText));
    
    
    print(z.toString())

edited Jul 25, 2022 at 9:57

answered Apr 27, 2019 at 7:06

Teddie

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1 Comment

Brian Tompsett - 汤莱恩 Over a year ago

Please add further explanation to your answer to assist readers. Code only answers are not always helpful.

Murhaf Sousli · Accepted Answer · 2015-11-07 11:50:20Z

1

The documentation is correct.

//if JSON is an array (starts with '[' )

List<Map> x = JSON.decode(responseText);
print(x[0]['title']);

//if JSON is not an array (starts with '{' )

Map z = JSON.decode(responseText);
print(z['content']);
print(z['id']);
print(z['title']);

answered Nov 7, 2015 at 11:50

Murhaf Sousli

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