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Version: 1.8.1

Migrate from MLAPI to Netcode for GameObjects

MLAPI is deprecated and no longer supported. Follow this guide to migrate from MLAPI to Netcode for GameObjects.

Back up your MLAPI project​

The transition from MLAPI to Netcode for GameObjects is significant and can cause issues with your current project. It's strongly recommended that you back up your existing MLAPI project before migration. You can do one or both of the following:

  • Create a copy of your entire project folder.
  • Use source control software, like Git.

Add the MLAPI Patcher to your MLAPI project​

Manually transitioning from MLAPI to Netcode for GameObjects will break all the component references in your project. You can use the MLAPI Patcher to automate the process and avoid breaking changes.

  1. Add the Netcode Patcher to your project. Open the Package Manager window in the Unity Editor and select Add package from Git URL... Use the following URL: https://github.com/Unity-Technologies/multiplayer-community-contributions/tree/release-0.1.0/com.unity.multiplayer.mlapi-patcher

Install the Netcode for GameObjects package​

Follow the installation guide to install Netcode for GameObjects. After installing the package, you'll see error messages in the console, which is expected because your project now has MLAPI and Netcode for GameObjects at the same time. Don't uninstall MLAPI yet - it's still required for the next step.

Installing Netcode for GameObjects also installs some other packages such as Unity Transport, Unity Collections, and Unity Burst.

The Burst package requires an Editor restart. After restarting, the Editor will ask you to enter safe mode at the next boot, which is normal behavior since your network code isn't compiling anymore.

Update script references​

You can use the MLAPI Patcher to automate updating your script references. Open the MLAPI Patcher by selecting Window > Netcode Patcher.

The Patcher will ask whether you're using the Installer version of MLAPI or the Source version. If you aren't sure which version of MLAPI you're using, you can check whether you have the Assets/MLAPI/Lib/MLAPI.dll file in your project. If you do, then you're using the Installer version of MLAPI. If you don't, then you're using the Source version of MLAPI.

In the Patcher window, select Installer or Source button:

  1. Select Installer.
  2. Select Update Script References.

After you complete the Update Script References process of the Patcher, the components in your project should have been updated to their new names.

There is also a Replace Type Names button in the Patcher window. This step is optional. It automatically renames old type names in your scripts to the API changes made in Netcode for GameObjects, saving you some time to manually rename it. It performs a simple global replace of some of the type names. You may want to manually do this process instead if you want more control over changes.

Remove old MLAPI versions​

Remove all the folders containing the existing non-package version of MLAPI from your project. Usually this means removing the Assets/MLAPI and Assets/Editor/MLAPI folders from the project.

Migrate your code to the new Netcode for GameObjects APIs​

info

Migrating your code is a long and manual process. If you run into difficulties, please join our Discord and we will support you.

As few breaking changes as possible were introduced as part of the transition from MLAPI to Netcode for GameObjects. However, a successful compilation still requires some changes.

NetworkVariable changes​

The NetworkVariable type is now generic only and the type specified in the generic needs to be a value type.

  1. Change your NetworkVariable* types into their generic counterpart. For example, NetworkVariableInt becomes NetworkVariable<int>, and NetworkVariableFloat becomes NetworkVariable<float>.
  2. Some of your types won't match the new type requirements for NetworkVariable<T>. If your type is a string, you can use FixedString32Bytes instead. Note that this type doesn't allow you to change the size of the string. For custom structs that only contain value types, you can implement INetworkSerializable, and it will work.
  3. For the other types, you'll need to create your own NetworkVariable. To achieve that, create a new class, inherit from NetworkVariableBase, and implement all the abstract members. If you already had custom NetworkVariable, read and write functions now use FastBuffer to read or write from and to the stream.

Scene management changes​

Scene management is now under the NetworkManager singleton. It can be accessed by:

var sceneManager = NetworkManager.Singleton.SceneManager;

There is now only one scene event instead of many: OnSceneEvent. You can subscribe to it and get scene events information from the SceneEvent class. In this class, you'll find the SceneEventType, which will give you precisions on what type of event is coming from the SceneManager.

Finally, the primary function to switch between scenes has changed to match the Unity SceneManager. Instead of SwitchScene, you now call LoadScene with two parameters: the scene name and the LoadSceneMode, which is the standard way to load a scene in Unity.

NetworkBehavior changes​

There are two main changes in NetworkBehavior:

  • NetworkStart method becomes OnNetworkSpawn, and OnNetworkDespawn was introduced to keep things symmetrical.
  • OnDestroy now needs to be overridden, since NetworkBehavior already uses it.

Changes in behavior​

Behavior changes are as minimal as possible, but there are two changes which are likely to cause errors in existing scripts:

  • NetworkManager now performs connection shut down when the application quits. If you were doing connection shutdown manually, you'll up with an error about disconnecting twice.
  • The library now fires all the OnValueChanged events from the NetworkVariable after the OnNetworkSpawn (previously known as NetworkStart) method has returned. You'll need to refactor any scripts depending on this order accordingly.

Upgrade RPCs​

The way RPCs are invoked has changed with this version of Netcode for GameObjects. Please read the documentation about RPCs and replace your existing RPCs with the new system.

Serialization​

The old INetworkSerializable interface has been replaced with a new INetworkSerializable interface. See INetworkSerializable.

The page also includes information on nested serial types.

SyncVars​

SyncVars have been removed in Netcode for GameObjects. Convert your existing SyncVars into NetworkVariables.

Remove the Patcher package​

After you're done upgrading your project, you can remove the MLAPI Patcher package from your project in the Unity Package Manager.

Troubleshooting​

Error: The type or namespace name 'MLAPI' can't be found

This error occurs if your project uses assembly definition (.asmdef) files. After switching to the package version, your assembly definition files need to reference com.unity.multiplayer.mlapi.runtime.

Error: The type or namespace name 'NetworkedBehaviour' can't be found

If you get an error message like this in the console, it's likely because your code has outdated APIs. Open the script indicated in the error message and update all APIs to the new names.

Error: SerializedObjectNotCreatableException: Object at index 0 is null

If this appears when you enter Play Mode or save a scene, close the Unity Editor and open it again and this should be gone.

Next steps​

After migrating to the Netcode for GameObjects package, you can review the following for what to do next: