NetworkList contains duplicate entries when its NetworkObject becomes visible to Client

[A1win]

Description

When network visibility of a NetworkObject changes from hidden to visible for a Client and the NetworkObject contains a NetworkList, the list contains duplicate entries when it's synced from Server to Client.

Steps to Reproduce

1. Instantiate a NetworkObject no, set no.CheckObjectVisibility = (clientId) => false, and spawn the NetworkObject (which is now hidden to all Clients).
2. On the Server, add an entry in a NetworkList that's attached to the NetworkObject. Check its contents on the Server.
3. Make the NetworkObject visible to a Client. Check the contents of the NetworkList on the Client. Notice that it contains the added entry in it twice instead of once.

I haven't reproduce this on a small test project and the steps above might not be exactly correct. Try adding/removing items from the NetworkList before and after making the NetworkObject visible to the Client and check if it's synced correctly.

Expected Outcome

NetworkList is always synchronized correctly from Server to Client.

Environment

• OS: Windows 10
• Unity version: 2021.3.19f1
• Netcode version: 1.2.0

[jeffreyrainy]

Hi @A1win ,

I haven't reproduce this on a small test project and the steps above might not be exactly correct.
I'm afraid this will be a required step.

I repro'ed the steps above, on our develop branch, and although I found a little improvement we could make, I was not able to repro your issue.

What I used:
SpawnedScript.cs

using Unity.Netcode;
using UnityEngine;

public class SpawnerScript : NetworkBehaviour
{
    public GameObject objectToSpawn;

    private SpawnedObjectScript spawnedObject;
    private NetworkObject networkObject;
    private bool readyToAdd = false;
    private bool readyToShow = false;

    private int nextValue = 0;

    void Update()
    {
        if (IsServer && Input.GetKeyDown(KeyCode.A))
        {
            Debug.Log("Pressed A");
            var instantiaedObject = UnityEngine.Object.Instantiate(objectToSpawn);
            networkObject = instantiaedObject.GetComponent<NetworkObject>();
            networkObject.CheckObjectVisibility = (clientID) => false;

            spawnedObject = instantiaedObject.GetComponent<SpawnedObjectScript>();
            networkObject.Spawn();

            readyToAdd = true;1
        }
        else if (readyToAdd && Input.GetKeyDown(KeyCode.B))
        {
            spawnedObject.list.Add(nextValue);
            nextValue++;

            readyToShow = true;
        }

        if (IsServer && readyToShow && Input.GetKeyDown(KeyCode.C))
        {
            networkObject.NetworkShow(1);
        }
    }
}

and
SpawnedObjectScript.cs

using Unity.Netcode;
using UnityEngine;

public class SpawnedObjectScript : NetworkBehaviour
{
    public NetworkList<int> list;

    public void Awake()
    {
        list = new NetworkList<int>();
        list.OnListChanged += foo;
    }

    public void foo(NetworkListEvent<int> le)
    {
        Debug.Log($"List changed {le.Type} {le.Index} {le.Value}");

        string str = "";

        foreach(var s in list)
        {
            str += $"{s}, ";
        }

        Debug.Log($"SpawnedObjectScript list now has {str}");
    }

    public override void OnNetworkSpawn()
    {
        string str = "";

        foreach(var s in list)
        {
            str += $"{s}, ";
        }

        Debug.Log($"SpawnedObjectScript spawned with {str}");
    }
}

I added an object with SpawnerScript.cs behaviour to my scene and pressed A, B, then C on the host, with one other client connected. What I observed is the correct behaviour, with logs:

==> log.1679401811.txt <==
Pressed A
SpawnedObjectScript spawned with
List changed Add 0 0
SpawnedObjectScript list now has 0,

==> log.1679401810.txt <==
SpawnedObjectScript spawned with 0,

One thing to note. 1.3.0 will be released soon and contains:

• NetworkShow() of NetworkObjects are delayed until the end of the frame to ensure consistency of delta-driven variables like NetworkList.

However, there's another place where this report becomes very useful is that it highlights an inconsistency in our processing of NetworkShow commands. Since you set CheckObjectVisibility = (clientId) => false, this should be overriding over NetworkShow and actually prevent the showing of the NetworkObject.

I'll put a PR for our team to discuss whether we want the visibility check to override NetworkShow.

On your side, though, you'll have to either try the code above or come up with similar small-scale repro to submit to us. You can also consider trying the develop branch that should be released as 1.3.0 soon. I expect this to fix your issue.

So, lot's of material here. TL;DR:

1. Your issue is most likely fixed in the upcoming 1.3.0, by the fix to NetworkShow
2. You have a small piece of code above if you want to repro and provide us with a sample snippet for it.
3. Even if the issue is fixed, you should not keep a constant (clientId) => false for CheckObjectVisibility. It might break in the future when we enforce it on NetworkShow

[LambdaCmplx]

Hi @jeffreyrainy,

Thanks for looking into this! We'll just need a little bit of time to go over what you suggested and put together a small test project that reproduces the issue. We'll keep you posted.

Thanks!

[mtarzwell]

Hello @LambdaCmplx any updates on how it's going with the test project? Thanks for letting us know what you found

[LambdaCmplx]

@mtarzwell Sorry, didn't have a chance to try it yet but aiming to do so in the next week or two.

[fluong6]

@LambdaCmplx Since we have not heard back from you, we are closing this ticket. Please create a new bug ticket if the issue still occurs.