The defult 'List' constructor isn't available when null safety is enabled. Flutter

Question

I am having a problem woth my code when connecting API's in flutter does anyone know how I can solve this error?

import 'package:ctrade/constants/strings.dart';
import 'package:ctrade/models/Users.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';

class Services {

  static const String url = 'https://linkhere.co.zw';

  static Future<List<Markets>> getMarkets() async{
    try{
      final response = await http.get(Uri.parse(url));
      if(200 == response.statusCode) {
        final List<Markets> markets = marketsFromJson(response.body);
        return markets;
      }else {
        return List<Markets>(); //error here
      }

    }catch(e){
      return List<Markets>(); //error here
    }
  }
}

score 2 · Accepted Answer · answered Jan 28 '22 at 15:14

2

Use a literal instead:

return [];

The compiler will use type inference to construct a list of the proper type.

Side note: Generally, Dart/Flutter is pretty helpful with error messages - The solution to your problem is in the message:

The default 'List' constructor isn't available when null safety is enabled. Try using a list literal, 'List.filled' or 'List.generate'.

answered Jan 28 '22 at 15:14

Michael Horn

3,819
9
22

1

documentation related to your answer: https://api.flutter.dev/flutter/dart-core/List/List.html – ישו אוהב אותך Jan 28 '22 at 15:20
Thank you! Sorry I'm a bit new to flutter, but is this the correct way of doing it? `return [Markets];` I am getting another error when I do it this way – Panashe Jan 28 '22 at 15:54
2

No, `return [];` – Richard Heap Jan 28 '22 at 16:02
1

Since the return type is already specified in the function declaration, you don't need to write the type at all - Dart can infer the type automatically. However, if you do want to make it explicit, @RichardHeap gave the right way to do it – Michael Horn Jan 28 '22 at 16:21
1

Thank you all very much! It worked – Panashe Jan 28 '22 at 16:49

The defult 'List' constructor isn't available when null safety is enabled. Flutter

1 Answers1