Real world In-scene NetworkObject parenting of players solution

We received the following issue in Github.

Issue:

When a player Prefab has a script that dynamically adds a parent to its transform, the client can't join a game hosted by another client. You can see orignal issue here

Steps to reproduce the behavior:

1. Set up basic networking game with at least one GameObject in a scene that isn't the player.
2. Add a script to the player Prefab that adds parenting to its transform via gameObject.transform.SetParent() in the Start() method.
3. Launch one instance of the game as Host.
4. Launch another instance and try to join as Client.

Solution:

If you want to do this when a player has first connected and all NetworkObjects (in-scene placed and already dynamically spawned by the server-host) have been fully synchronized with the client then we would recommend using the NetworkManager.SceneManager.OnSceneEvent to trap for the C2S_SyncComplete event.

Here is an example script that we recommend using to achieve this:

using Unity.Netcode;

public class ParentPlayerToInSceneNetworkObject : NetworkBehaviour
{   
    public override void OnNetworkSpawn()
    {
        if (IsServer)
        {
            // Server subscribes to the NetworkSceneManager.OnSceneEvent event
            NetworkManager.SceneManager.OnSceneEvent += SceneManager_OnSceneEvent;

            // Server player is parented under this NetworkObject
            SetPlayerParent(NetworkManager.LocalClientId);
        }
    }

    private void SetPlayerParent(ulong clientId)
    {
        if (IsSpawned && IsServer)
        {
            // As long as the client (player) is in the connected clients list
            if (NetworkManager.ConnectedClients.ContainsKey(clientId))
            {
                // Set the player as a child of this in-scene placed NetworkObject
                // We parent in local space by setting the WorldPositionStays value to false
                NetworkManager.ConnectedClients[clientId].PlayerObject.TrySetParent(NetworkObject, false);
            }
        }
    }

    private void SceneManager_OnSceneEvent(SceneEvent sceneEvent)
    {
        // OnSceneEvent is useful for many things
        switch (sceneEvent.SceneEventType)
        {
            // The C2S_SyncComplete event tells the server that a client-player has:
            // 1.) Connected and Spawned
            // 2.) Loaded all scenes that were loaded on the server at the time of connecting
            // 3.) Synchronized (instantiated and spawned) all NetworkObjects in the network session
            case SceneEventData.SceneEventTypes.C2S_SyncComplete:
                {
                    // As long as we aren't the server-player
                    if (sceneEvent.ClientId != NetworkManager.LocalClientId)
                    {
                        // Set the newly joined and synchronized client-player as a child of this in-scene placed NetworkObject
                        SetPlayerParent(sceneEvent.ClientId);
                    }
                    break;
                }
        }
    }
}

You should place this script on your in-scene placed NetworkObject (that is, the first GameObject) and do the parenting from it to avoid any timing issues of when it's spawned or the like. It only runs the script on the server-host side since parenting is server authoritative.

note

Remove any parenting code you might have had from your player Prefab before using the above script. Depending upon your project's goals, you might be parenting all players under the same in-scene placed NetworkObject or you might intend to have each player parenting unique. If you want each player to be parented under a unique in-scene placed NetworkObject then you will need to have the same number of in-scene placed NetworkObjects as your maximum allowed players per game session. The above example will only parent all players under the same in-scene placed NetworkObject. You can extend the above example by migrating the scene event code into an in-scene placed NetworkObject that manages the parenting of players (i,e. name it something like PlayerSpawnManager) as they connect, make the SetPlayerParent method public, and add all in-scene placed NetworkObjects to a public list of GameObjects that the PlayerSpawnManager will reference and assign player's to as they connect while also freeing in-scene placed NetworkObjects as players disconnect during a game session.