NetworkVariable.OnValueChanged is not called on the client unless the change took place while the object existed on the client

[TheCaveOfWonders]

Description

leaving original title and description for context.

NetworkShow does not set NetworkVariables

When we call NetworkHide on a dynamically created object, and later call NetworkShow, the object's network variables are not set.
NetworkHide will despawn and destroy the object on the client, so when the server calls NetworkShow, we are now creating a new object on the client, except this time the network variables don't get set.

Upon further testing, the issue turned out to be that NetworkVariable.OnValueChanged is not being called on the client, UNLESS the value changed while the network object existed on the client.

So if the client connects, and the network variable already had its value set on the server, OnValueChanged will not get called on the client.
Similarly, if the object is network hidden on the client side, when it becomes shown again, OnValueChanged is not called for the network variable; for a dynamically created network object it also gets destroyed on the client, not just network hidden.

Not sure if the parent hierarchy is playing a role here, but my network object is a child of another network object.

For the test, I have a Canvas that's an in-scene network object, then I dynamically (at run time) add a network object child to it (on the server), this network object has the behavior below, then I spawn this network object.

public class TestBehaviour : NetworkBehaviour
    {
        NetworkVariable<float> _networkVariable;

        [SerializeField]
        private TMP_Text _text;

        private void Awake()
        {
            _networkVariable = new NetworkVariable<float>();
            _networkVariable.OnValueChanged += OnNetworkVariableChanged;
        }

        private void OnNetworkVariableChanged(float previousValue, float newValue)
        {
          text.text = _networkVariable.Value.ToString();
        }

        private void Update()
        {
            if (_networkVariable != null)
            {
                _text.text = _networkVariable.Value.ToString();
            }
        }

        public override async void OnNetworkSpawn()
        {
            if (!NetworkManager.Singleton.IsServer)
            {
                return;
            }

            await new WaitForSeconds(10); // give time for client to connect.
            _networkVariable.Value = 69; // by now client connected, the client will have OnNetworkVariableChanged raised here.
            await new WaitForSeconds(10);
            NetworkObject.NetworkHide(1);
            _networkVariable.Value = 12; // here we change the value while the object is hidden for the client
            await new WaitForSeconds(10);
            NetworkObject.NetworkShow(1); // here we show the object to the client, since this object is dynamically created, a new instance will be created, BUT OnNetworkVariableChanged is never raised.
        }
    }

While inspecting this scene on the client side in the editor, I see everything behaving properly except for that OnNetworkVariableChanged method, it does not get raised unless a change took place while the network object existed.

This issue was not present in Netcode v1.0.0, I started experiencing it in v1.1.0

Actual Outcome

NetworkVariable.OnValueChanged is not called on the client unless the change took place while the object existed on the client.

Expected Outcome

NetworkVariable.OnValueChanged should be called when the variable's value changes, regardless if the change took place while the object existed on the client or not.

Environment

• OS: Win10
• Unity Version: 2022.1.23f1
• Netcode Version: 1.1.0

[jeffreyrainy]

From https://github.com/Unity-Technologies/com.unity.netcode.gameobjects/releases

1.1.0 should be
Oct 20 2c69184

But you list ba418fa5b600ad9eb61fab0575f12fbecc2c6520 which is

commit ba418fa5b600ad9eb61fab0575f12fbecc2c6520
Author: ashwini <36935028+ashwinimurt@users.noreply.github.com>
Date:   Fri Apr 1 11:25:32 2022 -0700
    chore: Bump NGO version to pre.7 (#1856)

So, I'm a bit puzzled. There's a six-month gap there. Can you specify which one correctly describe the code you are running?

Furthermore, in TestRunner, NetworkShowHideTest in PlayMode does

                // hide them on one client
                Show(mode == 0, false);
...
                m_NetSpawnedObject1.GetComponent<ShowHideObject>().MyNetworkVariable.Value = 3;
...
                Show(mode == 0, true);

and later asserts Assert.True(ShowHideObject.ClientTargetedNetworkObjects.Count == 3, $"Client-{clientNetworkManager.LocalClientId} should have 3 instances visible but only has {ShowHideObject.ClientTargetedNetworkObjects.Count}!");. Since this test is passing, NetworkVariables should be set
upon NetworkShow.

Can you please double-check?

[TheCaveOfWonders]

I will double check with a simpler object, sorry about the commit number that was auto-filled, I am on the 1.1.0 release.

[ashwinimurt]

MTT-5119

[TheCaveOfWonders]

Upon further testing, the issue turned out to be that NetworkVariable.OnValueChanged is not being called on the client, UNLESS the value changed while the network object existed on the client.

So if the client connects, and the network variable already had its value set on the server, OnValueChanged will not get called on the client.
Similarly, if the object is network hidden on the client side, when it becomes shown again, OnValueChanged is not called for the network variable; for a dynamically created network object it also gets destroyed on the client, not just network hidden.

Not sure if the parent hierarchy is playing a role here, but my network object is a child of another network object.

For the test, I have a Canvas that's an in-scene network object, then I dynamically (at run time) add a network object child to it (on the server), this network object has the behavior below, then I spawn this network object.

public class TestBehaviour : NetworkBehaviour
    {
        NetworkVariable<float> _networkVariable;

        [SerializeField]
        private TMP_Text _text;

        private void Awake()
        {
            _networkVariable = new NetworkVariable<float>();
            _networkVariable.OnValueChanged += OnNetworkVariableChanged;
        }

        private void OnNetworkVariableChanged(float previousValue, float newValue)
        {
          text.text = _networkVariable.Value.ToString();
        }

        private void Update()
        {
            if (_networkVariable != null)
            {
                _text.text = _networkVariable.Value.ToString();
            }
        }

        public override async void OnNetworkSpawn()
        {
            if (!NetworkManager.Singleton.IsServer)
            {
                return;
            }

            await new WaitForSeconds(10); // give time for client to connect.
            _networkVariable.Value = 69; // by now client connected, the client will have OnNetworkVariableChanged raised here.
            await new WaitForSeconds(10);
            NetworkObject.NetworkHide(1);
            _networkVariable.Value = 12; // here we change the value while the object is hidden for the client
            await new WaitForSeconds(10);
            NetworkObject.NetworkShow(1); // here we show the object to the client, since this object is dynamically created, a new instance will be created, BUT OnNetworkVariableChanged is never raised.
        }
    }

While inspecting this scene on the client side in the editor, I see everything behaving properly except for that OnNetworkVariableChanged method, it does not get raised unless a change took place while the network object existed.

[jeffreyrainy]

Hi @TheCaveOfWonders ,

First thing I need to mention:
public override async void OnNetworkSpawn()
This is definitely not supported. Any network-related notification, callback or API must return timely and not have any async/coroutine part to it. Consider it from the SDK point of view: What should the NetworkObject state be for those 10 seconds, if OnNetworkSpawn didn't finish ?

Good news, though, is that it is easy to convert to a traditional update-based approach. See below. I also used keydown instead of timers, to make testing easier.

        private void OnNetworkVariableChanged(float previousValue, float newValue)
        {
            Debug.Log($"OnNetworkVariableChanged {previousValue} -> {newValue}");
        }

        private void Update()
        {
            if (IsServer && Input.GetKeyDown(KeyCode.A))
            {
                _networkVariable.Value = 69; // the client will have OnNetworkVariableChanged raised here.
            }

            if (IsServer && Input.GetKeyDown(KeyCode.B))
            {
                NetworkObject.NetworkHide(1);
            }

            if (IsServer && Input.GetKeyDown(KeyCode.C))
            {
                _networkVariable.Value = 12; // here we change the value while the object is hidden for the client
            }

            if (IsServer && Input.GetKeyDown(KeyCode.D))
            {
                NetworkObject.NetworkShow(1);
                // here we show the object to the client, since this object is dynamically created, a new instance will be created, BUT OnNetworkVariableChanged is never raised.
            }
        }

        public override void OnNetworkSpawn()
        {
            Debug.Log($"OnNetworkSpawn {_networkVariable.Value}");
        }

Before looking at the logs the above is producing, let's answer this:

NetworkVariable.OnValueChanged is not called on the client

This is correct. OnValueChanged is only ever called if the value changed from what it was during OnNetworkSpawn. So, after a hide/show combo, you'll get a fresh OnNetworkSpawn with the new value and follow-up OnNetworkVariableChanged if the value changes from that.

I ran the above, pressed A, B, C, and D and got:
(duplicated because there was two player objects with this component)

pressed A
host
OnNetworkVariableChanged 0 -> 69
OnNetworkVariableChanged 0 -> 69
client
OnNetworkVariableChanged 0 -> 69
OnNetworkVariableChanged 0 -> 69
pressed B
pressed C
host
OnNetworkVariableChanged 69 -> 12
OnNetworkVariableChanged 69 -> 12
pressed D
client
OnNetworkSpawn 12
OnNetworkSpawn 12

I can forward this to our documentation team to check if we can make the documentation clearer, but my understanding is that by having your code check the value during OnNetworkSpawn, you can get the needed functionality.