Network Level Loading (Legacy)

(For new projects, you should use the new networking system introduced in 5.1. This information is for legacy projects using the old networking system.)

Below is a simple example of a way to load a level in a multiplayer game. It makes sure no network messages are being processed while the level is being loaded. It also makes sure no messages are sent, until everything is ready. Lastly, when the level is loaded it sends a message to all scripts so that they know the level is loaded and can react to that. The SetLevelPrefix function helps with keeping unwanted networks updates out of a new loaded level. Unwanted updates might be updates from the previous level for example. The example also uses groups to separate game data and level load communication into groups. Group 0 is used for game data traffic and group 1 for level loading. Group 0 is blocked while the level is being loaded but group 1 kept open, it could also ferry chat communication so that can stay open during level loading.

using UnityEngine;
using UnityEngine.Network;
using System.Collections;

[RequireComponent(NetworkView)]
public class ExampleScript : MonoBehaviour {
    string[] supportedNetworkLevels  = new[]{ "mylevel" };
    string disconnectedLevel = "loader";
    int lastLevelPrefix = 0;
    NetworkView networkView;    

    void Awake ()
    {
        // Network level loading is done in a separate channel.
        DontDestroyOnLoad(this);
        networkView = new NetworkView ();
        networkView.group = 1;
        Application.LoadLevel(disconnectedLevel);
    }
    
    void OnGUI ()
    {
        if (Network.peerType != NetworkPeerType.Disconnected)
        {
            GUILayout.BeginArea(Rect(0, Screen.height - 30, Screen.width, 30));
            GUILayout.BeginHorizontal();
            
            foreach (var level in supportedNetworkLevels)
            {
                if (GUILayout.Button(level))
                {
                    Network.RemoveRPCsInGroup(0);
                    Network.RemoveRPCsInGroup(1);
                    networkView.RPC( "LoadLevel", RPCMode.AllBuffered, level, lastLevelPrefix + 1);
                }
            }
            GUILayout.FlexibleSpace();
            GUILayout.EndHorizontal();
            GUILayout.EndArea();
        }
    }
    
    [RPC]
    IEnumerator LoadLevel (string level, int levelPrefix)
    {
        lastLevelPrefix = levelPrefix;
        
        // There is no reason to send any more data over the network on the default channel,
        // because we are about to load the level, thus all those objects will get deleted anyway
        Network.SetSendingEnabled(0, false);    
        
        // We need to stop receiving because first the level must be loaded first.
        // Once the level is loaded, rpc's and other state update attached to objects in the level are allowed to fire
        Network.isMessageQueueRunning = false;
        
        // All network views loaded from a level will get a prefix into their NetworkViewID.
        // This will prevent old updates from clients leaking into a newly created scene.
        Network.SetLevelPrefix(levelPrefix);
        Application.LoadLevel(level);
        yield return;

        // Allow receiving data again
        Network.isMessageQueueRunning = true;
        // Now the level has been loaded and we can start sending out data to clients
        Network.SetSendingEnabled(0, true);

        var gameObjects = FindObjectsOfType(GameObject) as GameObject[];
        foreach (var go in gameObjects)
            go.SendMessage("OnNetworkLoadedLevel", SendMessageOptions.DontRequireReceiver); 
    }
    
    void OnDisconnectedFromServer ()
    {
        Application.LoadLevel(disconnectedLevel);
    }
}

C# example script

var supportedNetworkLevels : String[] = [ "mylevel" ];
var disconnectedLevel : String = "loader";
private var lastLevelPrefix = 0;

function Awake ()
{
    // Network level loading is done in a separate channel.
    DontDestroyOnLoad(this);
    networkView.group = 1;
    Application.LoadLevel(disconnectedLevel);
}

function OnGUI ()
{
    if (Network.peerType != NetworkPeerType.Disconnected)
    {
        GUILayout.BeginArea(Rect(0, Screen.height - 30, Screen.width, 30));
        GUILayout.BeginHorizontal();
        
        for (var level in supportedNetworkLevels)
        {
            if (GUILayout.Button(level))
            {
                Network.RemoveRPCsInGroup(0);
                Network.RemoveRPCsInGroup(1);
                networkView.RPC( "LoadLevel", RPCMode.AllBuffered, level, lastLevelPrefix + 1);
            }
        }
        GUILayout.FlexibleSpace();
        GUILayout.EndHorizontal();
        GUILayout.EndArea();
    }
}

@RPC
function LoadLevel (level : String, levelPrefix : int)
{
    lastLevelPrefix = levelPrefix;

        // There is no reason to send any more data over the network on the default channel,
        // because we are about to load the level, thus all those objects will get deleted anyway
        Network.SetSendingEnabled(0, false);    

        // We need to stop receiving because first the level must be loaded first.
        // Once the level is loaded, rpc's and other state update attached to objects in the level are allowed to fire
        Network.isMessageQueueRunning = false;
        
        // All network views loaded from a level will get a prefix into their NetworkViewID.
        // This will prevent old updates from clients leaking into a newly created scene.
        Network.SetLevelPrefix(levelPrefix);
        Application.LoadLevel(level);
        yield;

        // Allow receiving data again
        Network.isMessageQueueRunning = true;
        // Now the level has been loaded and we can start sending out data to clients
        Network.SetSendingEnabled(0, true);

        for (var go in FindObjectsOfType(GameObject))
            go.SendMessage("OnNetworkLoadedLevel", SendMessageOptions.DontRequireReceiver); 
}

function OnDisconnectedFromServer ()
{
    Application.LoadLevel(disconnectedLevel);
}

@script RequireComponent(NetworkView)

JS example script