fromJson and toJson

app.dart

  static AppState fromJson(dynamic json) {
    var tasks = <String, Task>{};
    if (json is Map && json['tasks'] is Map) {
      json['tasks'].forEach((uuid, jsonTask) {
        var task = Task.fromJson(jsonTask);
        tasks[task.uuid] = task;
      });
    }
    return AppState(status: Status.noParam(StatusKey.ListTask), tasks: tasks);
  }

  dynamic toJson() {
    Map<String, dynamic> ret = <String, dynamic>{};
    tasks.forEach((uuid, task) {
      ret[uuid] = task.toJson();
    });
    return {"tasks": tasks};
  }