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rxdart_devtools

Display complex values

The DevTools panel shows the latest value of each tracked stream in a Current value card, and prior values in the Event log. The way a value is rendered depends on how it serializes.

How values are serialized

When a value flows through a tracked stream, the runtime encodes it as a string for transport to the DevTools UI. The encoder calls jsonEncode with a toString() fallback for anything that can’t be serialized:

jsonEncode(value, toEncodable: (nonEncodable) => nonEncodable.toString());

On the UI side, the panel tries to JSON-decode that string. If the decoded result is a Map or List, it’s rendered as a pretty-printed JSON tree. Anything else is rendered as plain text.

What this means for your classes

Value typeResult on the panel
num, bool, String, nullShown as the primitive value.
Map<String, …> / List<…> of JSON-encodable valuesPretty-printed JSON tree.
Custom class with a toJson() methodtoJson() is called; result is rendered as JSON.
Custom class without a toJson() methodFalls back to toString(). By default that’s Instance of 'YourClass'.
DateTime, Uri, enums, etc.Falls back to toString() (e.g., 2026-06-27 14:32:00.000).

The fallback only applies at the leaf where serialization can’t continue. A Map<String, User> where User has no toJson() still renders as a structured map — each User becomes the result of User.toString() inside the otherwise-structured tree.

Make a custom class render as JSON

Add a toJson() method to your class. Any of these work:

Hand-written

class User {
  User({required this.name, required this.age});


  final String name;
  final int age;


  Map<String, dynamic> toJson() => {'name': name, 'age': age};
}

With json_serializable

@JsonSerializable()
class User {
  User({required this.name, required this.age});


  final String name;
  final int age;


  Map<String, dynamic> toJson() => _$UserToJson(this);
}

With freezed

freezed generates a toJson() automatically when you opt in. No manual work needed once the model is annotated.

Limitations

Dart doesn’t support runtime reflection in Flutter, so the runtime can’t automatically introspect the fields of a class it doesn’t know about. If you want structured JSON for your domain objects, you have to provide toJson() — either by hand or via code generation. There’s no toEncodable trick that can unfold arbitrary objects into maps for you; this is a Dart-level constraint, not a rxdart_devtools limitation.