Flutter: SyntaxError: Unexpected token < in JSON at position 0

Question

I need to fetch data from API but my try-catch fails with SyntaxError: Unexpected token < in JSON at position 0.

Code:

    String problems;
     try {
         final response = await http.get('http://myURL',headers: {"Accept": "application/json"});
      log("after http");
      if (response.statusCode == 200) {
        final data = json.decode(response.body);
        problems = data["IsSuccess"];
        return problems.toString();
      } else {
        throw Exception('Failed to load status data');
      }
    } catch (exc) {
      log("catch:" + exc.toString());
    }
  }

Solution

NetService:

import 'dart:convert';

import 'package:http/http.dart' as http;


class NetService {
  /* ---------------------------------------------------------------------------- */
  static Future<T> getJson<T>(String url) {
    return http.get(Uri.parse(url))
      .then((response) {
        if (response.statusCode == 200) {
          return jsonDecode(response.body) as T;
        }
        print('Status Code : ${response.statusCode}...');
        return null;
      })
      .catchError((err) => print(err));
  }
}

Main:

import 'dart:async';

import 'package:_samples2/networking.dart';

class IOT {
  List data;

  FutureOr<void> fetchMeasurements() async {
    await NetService.getJson<Map<String, dynamic>>('http://iot.productio.net/api/Measurement/GetMeasurements')
      .then((response) {
        data = (response != null && response['IsSuccess'])
          ? response['Entity']
          : null;
      })
      .whenComplete(() => print('Fetching done!....'));
  }
}
void main(List<String> args) async {
  var iot = IOT();
  await iot.fetchMeasurements();
  print(iot.data.take(3).toString());
}

Result:

Fetching done!....
({Id: 21315, MeasurementDate: 2021-02-18T22:06:20.8365195, Temperature: 20.6, Humidity: 36.8, Misto: loznice}, {Id: 21314, MeasurementDate: 2021-02-18T22:01:19.1337516, Temperature: 20.6, Humidity: 37.0, Misto: loznice}, {Id: 21313, MeasurementDate: 2021-02-18T21:56:18.1720883, Temperature: 20.6, Humidity: 36.9, Misto: loznice})

Comments

[Andrej]

You got the error because your api returned html not json.

[Altimus Prime]

Please include some explanation with your answer.

[Admin]

I created a new project just with your code This appears: Restarted application in 11 308ms. XMLHttpRequest error. Fetching done!.... TypeError: Cannot read property 'Symbol(dartx.take)' of null at main$ (http://localhost:54159/packages/jsontest/main.dart.lib.js:9‌​1:40) at main$.next (<anonymous>) ....

[Ουιλιαμ Αρκευα]

This seems to be an error from your configuration. (1) Check if you can get response from http://iot.productio.net/api/Measurement/GetMeasurements in your browser, (2) What's your system info?, (3) Have you checked this post?

[Admin]

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.