Unable to parent NetworkObject to a NetworkObject only on client

[Conundroy]

Description

Unable to parent NetworkObject to a NetworkObject only on client.

Reproduce Steps

1. Host spawns NetworkObject (DestroyedWithScene = true) and parent it via script.

Actual Outcome

Host:

• Scene
  • Parent NetworkObject
    • Child NetworkObject

Client:

• Scene
  • Parent NetworkObject
  • Child NetworkObject

Expected Outcome

Host:

• Scene
  • Parent NetworkObject
    • Child NetworkObject

Client:

• Scene
  • Parent NetworkObject
    • Child NetworkObject

Environment

• OS: Windows
• Unity Version: 6000.0.22f1
• Netcode Version: 2.0.0

Additional Context

Works if I spawn and parent in editor, probably has something to do with DesroyedWithScene set to true?

Update: Works when I downgrade to v1.11.0

[NoelStephensUnity]

@Conundroy
If you could post the associated script it would help me provide better guidance on this issue.
Make sure you have spawned both NetworkObject instances before you attempt to parent them. Otherwise, if you are parenting them prior to spawning then that will not synchronize properly.

Order of Operations:

• Instantiate and spawn parent
• Instantiate and spawn child
  • Get the NetworkObject of the child.
  • Invoke NetworkObject.TrySetParent

Let me know if this resolves your issue or if not then if you could provide me with a replication project or the script that you are using to instantiate, spawn, and parent the two objects it would be helpful.

[Fobri]

I have the same issue, it started appearing when I upgraded from 1.8 to 2.0.
The scenario I have is very simple, a networkbehaviour instantiates and spawns an instance of a networkobject, and then parents it under itself called in OnNetworkSpawn.
Simplified pseudocode of what I'm doing below.

override void OnNetworkSpawn()
{
   var instance = Instantiate(prefab);
   instance.GetComponent<NetworkObject>().Spawn();
   instance.transform.parent = transform;
}

The object gets correctly parented on server and also late joining clients, but for clients currently in the game the parenting never happens.

[Conundroy]

@NoelStephensUnity

Here's the script on the parent object/game manager:

public override void OnNetworkSpawn()
{
    if (IsHost) GenerateItems();
    base.OnNetworkSpawn();
{

void GenerateItems()
{
    Mesh mesh = Map.Instance.GetComponentInChildren<MeshFilter>().sharedMesh;
    Bounds bounds = mesh.bounds;

    // Spawn coins
    for (int i = 0; i < numCoins; i++)
    {
        TrySpawnObject(coin, mesh);
    }
}

void TrySpawnObject(GameObject objectPrefab, Mesh mesh)
{
    int randomTriangle = Random.Range(0, mesh.triangles.Length / 3) * 3;  // Choose a random triangle

    Vector3 v0 = mesh.vertices[mesh.triangles[randomTriangle]];
    Vector3 v1 = mesh.vertices[mesh.triangles[randomTriangle + 1]];
    Vector3 v2 = mesh.vertices[mesh.triangles[randomTriangle + 2]];

    // Compute the center of the triangle (polygon face)
    Vector3 center = (v0 + v1 + v2) / 3f;

    // Get the normal of the triangle
    Vector3 normal = Vector3.Cross(v1 - v0, v2 - v0).normalized;

    // Apply random offset in the x and z directions within the range (-3, 3)
    Vector3 randomOffset = new Vector3(
        Random.Range(-3, 3),
        0f, // No offset in the Y direction
        Random.Range(-3, 3)
    );

    Vector3 spawnPosition = center + randomOffset;


    // Directly instantiate at the calculated position
    GameObject newItem = Instantiate(objectPrefab, spawnPosition, Quaternion.identity);
    newItem.GetComponent<NetworkObject>().Spawn(true);
    newItem.GetComponent<NetworkObject>().TrySetParent(transform);
}

This works as intended in v1.11.0.

[NoelStephensUnity]

Hmmm...generally speaking...instantiating and spawning in the middle of spawning is not recommended as it can lead to issues down the road.

Just out of curiosity, have you tried changing the OnNetworkSpawn to OnNetworkPostSpawn?
This would assure all components had finished running through their spawn process prior to spawning more things and parenting them under the NetworkObject that just finished spawning. There are some updates in v2.0.0 that leverage from NetworkPreSpawn and NetworkPostSpawn ordering which could have impacted spawing in the middle of spawning.

[Fobri]

This is the first time I'm hearing that its not recommended to spawn things inside OnNetworkSpawn. How are you supposed to spawn things on server when it initializes then?
My entire server logic gets kicked off in a OnNetworkSpawn that loads a map from disk, and populates it by instantiating and spawning objects. So far I haven't had any issue with that. Perhaps because it's an in-scene placed object?

I did also try OnNetworkPostSpawn for this specific issue, and it didn't change anything.

[NoelStephensUnity]

@Fobri
I will take a look to see if there is a bug here, but the issue isn't that you can't spawn things during OnNetworkSpawn or OnNetworkPostSpawn but that if during spawning something you spawn another NetworkObject that will be parented under the NetworkObject currently being spawned.
However, I will investigate this issue further to see if I can replicate it on my end too and if there was a recent update that is the cause of this issue.
👍

[NoelStephensUnity]

I have the same issue, it started appearing when I upgraded from 1.8 to 2.0. The scenario I have is very simple, a networkbehaviour instantiates and spawns an instance of a networkobject, and then parents it under itself called in OnNetworkSpawn. Simplified pseudocode of what I'm doing below.

override void OnNetworkSpawn()
{
   var instance = Instantiate(prefab);
   instance.GetComponent<NetworkObject>().Spawn();
   instance.transform.parent = transform;
}

The object gets correctly parented on server and also late joining clients, but for clients currently in the game the parenting never happens.

Have you tried setting the transform on a NetworkBehaviour (OtherNetworkBehaviour below) of the instantiated prefab and parenting it within the OnNetworkPostSpawn of the NetworkBehaviour on the newly instantiated prefab?

override void OnNetworkSpawn()
{
   var instance = Instantiate(prefab);
   instance.GetComponent<OtherNetworkBehaviour>.SetTargetParent(transform);
   instance.GetComponent<NetworkObject>().Spawn();
}

And then on OtherNetworkBehaviour:

    private Transform m_TargetParent;

    public void SetTargetParent(Transform targetParent)
    { 
        m_TargetParent = targetParent; 
    }

    protected override void OnNetworkPostSpawn()
    {
        if (IsServer) 
        {
            NetworkObject.TrySetParent(m_TargetParent);
        }
        base.OnNetworkPostSpawn();
    }

This will assure that when you are parenting the newly spawned object instance is fully spawned prior to parenting it.

[marcusx2]

I have the same issue. If you spawn something and then on the client make a serverrpc call to set the parent, the parent will change on the server and client for all available clients and late joiners. However, if the server does the parent change on its own (without a serverrpc) the parent only changes on the server and not on any already available clients (late joiners will have the correct parent though).

[EmandM]

@marcusx2 Do you have the script of how your server is doing the parent change? If the client is not fully connected and synchronized when the parent is changed then the parent change message can be lost.

[marcusx2]

Do you have the script of how your server is doing the parent change? If the client is not fully connected and synchronized when the parent is changed then the parent change message can be lost.

@EmandM It's nothing special. It's a NetworkBehaviour script attached to a network object. I check if it's the server or if it's the client OnNetworkSpawn. If it's the server I spawn and call TrySetParent, that is all. The parenting doesn't work for clients that are already connected, only late joiners. Maybe if I use NetworkPostSpawn? Haven't tried it. But anyways, it's a bug. It doesn't make sense to think that the message can be lost, when late joiners are correctly reparented.

[NoelStephensUnity]

@marcusx2 @Conundroy
I have targeted the problematic area for this issue within the ParentSyncMessage where it is not properly deferring the message when the parent is not spawned yet and have a pending fix that I will be posting a PR for shortly. Since this issue is relatively high, I am going to see if we can have a v2.3.1 patch for this issue (will find out Monday and you should see a PR created for this issue by sometime on Monday).

[NoelStephensUnity]

Closing as #3401 resolved this issue.
This issue will be resolved in the hot-fix patch v2.3.1 update which should be available very soon.

[NoelStephensUnity]

v2.3.1 is now available.