Can't read float array into C# from JSON using Simple JSON

Questions & Answers
1

I am trying to integrate ROS and Unity using this repository. Here is the JSON message I received using rosbridge websocket server :

{"topic": "/danaus05/motion_manager/traj_spline", 
"msg": 
{"header":
 {"stamp": 
{"secs": 4701, 
"nsecs": 820000499}, 
"frame_id": "", "seq": 131}, 
"knot_times": [0.0, 0.022315455600619316], 
"sample_dt": 0.10000000149011612, 
"order": 13, 
"coefficients": [10.421317100524902, 0.42876696586608887, 0.0, -4.028246920056988e-13, 9.025688182950908e-12, -7.67222327331283e-26, 3.820084571512169e-24, -4.8910171295495195e-23, -4.0375719823897506e-36, 1.0721875680448314e-34, -9.609371526029533e-34, 0.0, 0.0, 0.0, -18.514339447021484, -0.9034151434898376, 0.0, -1.9118333218631767e-13, 4.2836528595102674e-12, 1.616543134702147e-25, -8.048946608918099e-24, 1.0305409390922075e-22, -1.916259013748819e-36, 5.088674866680114e-35, -4.560672880415734e-34, 0.0, 0.0, 0.0, 0.21829719841480255, 1.1102230246251565e-16, 0.0, 0.0, 0.0, -1.9866208328732932e-41, 9.891499612960662e-40, -1.266450251934222e-38, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, -1.127668857574463, 0.0, -1.3376730279013316e-12, 3.996252981308679e-11, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}, 
"op": "publish"}

I’m using the SimpleJSON.cs as the JSONNode class. And here is the class that I created. The execution stops at line 31:

using ROSBridgeLib.std_msgs;
using SimpleJSON;
using UnityEngine;

/**
 * Define a Spline message.
 * /danaus05/motion_manager/traj_spline
 * 
 */

namespace ROSBridgeLib
{
    namespace teleoperationsandbox
    {
        public class SplineMsg : ROSBridgeMsg
        {
            private HeaderMsg _header;
            private int _seq, _secs, _nsecs;
            private TimeMsg _stampmsg;
            private byte _order;
            private float _sample_dt;
            private float[] _knot_times;
            private string _coefficients;
            int i;

            public SplineMsg(JSONNode msg)
            {
                //_seq = _header.GetSeq();
                //_stampmsg = _header.GetTimeMsg();
                //_secs = _stampmsg.GetSecs();
                //_nsecs = _stampmsg.GetNsecs();
                _order = byte.Parse(msg["order"]);
                Debug.Log(_order);
                _knot_times = float.Parse(msg["knot_times"]);
                //_coefficients = float.Parse(msg["coefficients"]).ToString();

            }

            public static string getMessageType()
            {
                return "quadrotor_msgs/Spline";
            }

            public float GetOrder()
            {
                return _order;
            }

            public string GetCoefficients()
            {
                return _coefficients;
            }

            public string GetKnotTimes()
            {
                return _knot_times;
            }    

            public override string ToString()
            {
                return "quarotor_msgs/Spline [seq=" + ",  secs=" + ", nsecs=" +
                    ", order=" + _order + ", knot_times=" + _knot_times + ", coefficients=" + _coefficients + "]";
            }

            public override string ToYAMLString()
            {
                return "{\"seq\": " + ", \"secs\": " + ", \"nsecs\": "+", \"order\": " + _order + ", \"knot_times\": " + _knot_times + ", \"coefficients\": " + _coefficients + "}";
            }
        }
    }
}
2

assuming JSONNode msg is in fact the msg sub-dictionary in the json object, that should work.
but are you sure that’s the case ?
if the overall message is being passed in, then you would need to access msg["msg"]["order"].

3

You can’t parse a JSONNode into a byte. JSONNode is a class and in the case of the “order” element it represents a “JSONData” instance. Each JSONNode as casting properties. Next thing is “knot_times” is an array which is represented by a JSONArray instance. You would need to use either a loop that or use Linq.

You should do something like this:

using System.Linq;

public SplineMsg(JSONNode msg)
{
    _order = (byte)msg["order"].AsInt;
    _knot_times = msg["knot_times"].Children.Select(n=>n.AsFloat).ToArray();
}