Instance.OnFlutterMessage event doesn't return callback

[mhanzla80]

Describe the bug

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.EventSystems;
using FlutterUnityIntegration;
using UnityEngine.UI;

public class NameUpdater : MonoBehaviour, IEventSystemHandler
{

    void Start()
    {
        GetComponent<Text>().text = "Zaihd Khan";
    }

    private void OnEnable()
    {
        UnityMessageManager.Instance.SendMessageToFlutter("OnEnable called");

        UnityMessageManager.Instance.OnFlutterMessage += Instance_OnFlutterMessage;
    }
    
    private void OnDisable()
    {
        UnityMessageManager.Instance.SendMessageToFlutter("OnDisable called");

        UnityMessageManager.Instance.OnFlutterMessage -= Instance_OnFlutterMessage;
    }

    private void Instance_OnFlutterMessage(MessageHandler handler)
    {
        UnityMessageManager.Instance.SendMessageToFlutter(string.Format("id: {0} name:{1} seq: {2}", handler.id, handler.name, handler.seq));

        Invoke("updatedFromOnFlutterMessaage", 10);
    }

    void updatedFromOnFlutterMessaage() {
        UnityMessageManager.Instance.SendMessageToFlutter("updatedFromOnFlutterMessaage called");

        UpdateName("Instance_OnFlutterMessage Noor Ali");
    }

    // Update is called once per frame
    void Update()
    {
        
    }

    // This method is called from Flutter
    public void UpdateName(String message)
    {
        UnityMessageManager.Instance.SendMessageToFlutter("UpdateName called");

        GetComponent<Text>().text = message;
    }
}

Expected behavior
Instance_OnFlutterMessage. should be called wen i postJsonMessage from flutter

Unity:

• Version 2021.3.8f1

void onPressed() {
    _unityWidgetController?.postJsonMessage(
      'MyText',
      'UpdateName',
      {'name': 'AhmadKan'},
    );
  }

It does print {"name":"AhhmadKhan"} on screen

[timbotimbo]

These events seem to be legacy code that hasn't been used or referenced in a couple of years.

The current message appoach is part of Unity-as-a-Library and is similar to GameObject.SendMessage.
You directly call a function on a Gameobject's monobehaviour, which the MessageManager script can't intercept.
So I don't think an event that registers all messages from Flutter is currently possible.