"Unexpected Character" on Decoding JSON

Question

The following 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);
  }

Error produced by Android Studio:

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

Any idea how to make it work?

This is the output of the Json as produced by Redux.

Answer 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.

Answer 2

I don't know if that's the case, but I got a similar error when me JSON looks like this

[ { ... }, ]

and not like this

[ { ... } ]

The comma was causing the issue.

Answer 3

If Anyone came here and your are using dio package to call http request you need to set responseType to plain

 BaseOptions options = new BaseOptions(
    baseUrl: "<URL>",
    responseType: ResponseType.plain
  );

Answer 4

I also have similar type of error, Be make sure that the argument of .decode method shouldn't be empty object.

try {
if(json["todos"].isNotEmpty) {
List<Todo> data = codec.decode(json["todos"]);
}
if(json["todos"].isNotEmpty) {
VisibilityFilter filter = codec.decode(json['visibilityFilter']);
}
}
catch(e) {
print(e);
}

Do try this, hope it will work for you.