“Unexpected Character” on Decoding JSON

问题:

This is the code,

    static TodoState fromJson(json) {
          JsonCodec codec = new JsonCodec();
            List<Todo> data = codec.decode(json["todos"]);
            VisibilityFilter filter = codec.decode(json['visibilityFilter']);


     return new TodoState(todos: data,
                          visibilityFilter: filter);
  }

The error that Android Studio gives to me is below

[VERBOSE-2:dart_error.cc(16)] Unhandled exception:
FormatException: Unexpected character (at character 3)

Any idea how to make it works?

This is the output of of the Json as Redux Give me

回答1:

There's a problem with your code as well as the string you're trying to parse. I'd try to figure out where that string is being generated, or if you're doing it yourself post that code as well.

Valid Json uses "" around names, and "" around strings. Your string uses nothing around names and '' around strings.

If you paste this into DartPad, the first will error out while the second will succeed:

import 'dart:convert';

void main() {
  JsonCodec codec = new JsonCodec();
  try{
    var decoded = codec.decode("[{id:1, text:'fdsf', completed: false},{id:2, text:'qwer', completed: true}]");
    print("Decoded 1: $decoded");
  } catch(e) {
    print("Error: $e");
  }

  try{
    var decoded = codec.decode("""[{"id":1, "text":"fdsf", "completed": false},{"id":2, "text":"qwer", "completed": true}]""");
    print("Decoded 2: $decoded");
  } catch(e) {
    print("Error: $e");
  }
}

The issue with your code is that you expect the decoder to decode directly to a List. It will not do this; it will decode to a dynamic which happens to be a List<dynamic> whose items happen to be Map<String, dynamic>.

See flutter's Json documentation for information on how to handle json in Dart.