Dart - 当我们输入的密钥错误时，我可以处理来自 json.decode 的 null 值吗

Question

Can we handle null value output from json.decode? I already try using if else function, but it doesn't really works well.

import 'dart:convert';
var typeCat = "WrongKey";
var endPoint = "WrongKey";

void main() async {
  final base = RetryClient(http.Client());
  String outputJSON = await base.read(
      Uri.parse("http://estra-api.herokuapp.com/api/${typeCat}/${endPoint}"));
  final link_decode = json.decode(outputJSON)["link"] as String;
  final text_decode = json.decode(outputJSON)["text"] as String;
  print(link_decode);
  print(text_decode);
}

Is there anything I can do with these codes?

Answer 1

I can't be 100% sure since you didn't share the full error message, but the problem seem to be that you're trying to cast to a non-nullable String a value that can possibly be null .

  final link_decode = json.decode(outputJSON)["link"] as String?;
  final text_decode = json.decode(outputJSON)["text"] as String?;

and if you want to assign a default value for them you can also:

  final link_decode = json.decode(outputJSON)["link"] ?? 'default';
  final text_decode = json.decode(outputJSON)["text"] ?? 'default';

This will allow link_decode and text_decode to have null as value

Try this and if you don't succede share the error message.