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Upgrade MLAPI to Netcode for GameObjects

Use this guide to upgrade from MLAPI 0.1.0 to Netcode for GameObjects (Netcode) 1.0.0.

Upgrade to Netcode for GameObjects

It is recommended to upgrade to Netcode from MLAPI as soon as possible. MLAPI is not maintained and will not have future updates. MLAPI should be considered a deprecated product.

Backup your MLAPI project#

important

Consider this step a required: Upgrading to the package version of Netcode can cause issues with your current project. The new version modifies files and locations that are drastically different than previous MLAPI versions.

Backup your project using the following recommended methods:

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

We recommend using both methods to backup your project. This gives you a copied project and tracking through committed changes and history.

Use the Upgrade Tool on your MLAPI project#

Manually upgrading from the .dll version installed by MLAPI to the new package version breaks all MLAPI component references in your scenes and prefabs. Netcode references components using GUIDs that work differently for packages than for .dlls.

To help with the upgrade process to Netcode, we have created an upgrade tool.

To start upgrading, add the upgrade tool to your project by using the Add package from git URL.. option in the Package Manager window. Use the following URL:

https://github.com/Unity-Technologies/mlapi-community-contributions.git?path=/com.unity.multiplayer.mlapi-patcher

After installing the patcher package, you can continue the upgrade process.

Install the Netcode Package#

Follow the installation guide to install Netcode.

After installing the package, you will have error messages in the console, which is expected behavior because your project now contains MLAPI and Netcode at the same time. This will be remedied by the end of this guide.

Installing the Netcode package will also install some other packages such as Unity Transport, Unity Collections, Unity Burst etc.

The Burst package requires an Editor restart. So restart your Unity after the installation. Unity will ask you to enter Fail Safe mode at the next boot, which is normal behaviour since all your network code is not compiling anymore.

warning

Do not remove the old version of MLAPI yet. It will still be used in the next step.

Updating Script References#

Open the Netcode patcher window by selecting Window > Netcode Patcher in the menu bar. The patcher will ask you whether you are using the Installer version of MLAPI or the Source version.

Previously there were two major ways to use MLAPI in projects. You could either download a release version of MLAPI using the MLAPI installer or manually copy the source files into your project.

tip

If you are not sure which way of MLAPI you are using check whether you have the Assets/MLAPI/Lib/MLAPI.dll file in your project. If that's the case you are using the Installer version.

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 Netcode components on your Prefabs and GameObjects 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, 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 older 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.

Upgrade your code to the new Netcode APIs#

info

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

The Unity Multiplayer team tried to keep most of the MLAPI intact in Netcode. However, a successful compilation still requires some changes.

NetworkVariable changes#

NetworkVariable type is now generic only and the type specified in the generic needs to be a value type. First, change all your NetworVariable* types for their generic counterpart. For example, NetworkVariableInt becomes NetworkVariable<int>, NetworkVariableFloat becomes NetworkVariable<float> and so on. Now, some of your types (string, for example) will not match the new type requirements for NetworkVariable<T>. If your type is a string, you can use FixedString32Bytes instead. One should note that this type does not 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. Finally, for the other types, you will 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 uses our FastBuffer to read or write from and to the stream.

Scene Management changes#

The scene management had some changes unifying the way users uses it. First, it is now under the NetworkManager Singleton. Consequently, you directly access it by:

var sceneManager = NetworkManager.Singleton.SceneManager;

Next, 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 will find the SceneEventType, which will give you precisions on what type of event is coming from the Scene Manager. Finally, the primary function to switch between scenes has changed to match the Unity Scene Manager. 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. First, the NetworkStart method becomes OnNetworkSpawn, and we introduced OnNetworkDespawn to keep things symmetrical. Second, OnDestroy now needs to be overridden since NetworkBehavior already uses it.

Changes in behavior#

We tried to keep the behavior changes minimal but two changes may cause errors in your scripts. First, the NetworkManager now does its connection shut down when the application quits. If you were doing it by yourself, you would end up with an error saying that you tried to disconnect twice. Second, the library now fires all the OnValueChanged events from the NetworkVariable after the OnNetworkSpawn (previously known as NetworkStart) method has returned. You will need to refactor any scripts depending on this order accordingly.

Upgrade RPCs#

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

Serialization#

We replaced the old INetworkSerializable interface with a new INetworkSerializable interface. The interface works a bit different. See INetworkSerializable.

The page also includes information on nested serial types.

SyncVars#

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

Remove the Patcher Package#

After you are done upgrading your project, you can remove the Netcode Patcher package from your project in the Unity Package Manager as it is no longer needed.

Troubleshooting#

Error: The type or namespace name 'MLAPI' could not be found

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

Error: The type or namespace name 'NetworkedBehaviour' could not be found

If you get an error message like this (or for another Netcode type than NetworkedBehaviour) in the console it is most likely because your code contains outdated APIs. Open the script indicated in the error messagea and update all APIs to the new names.

Error: SerializedObjectNotCreatableException: Object at index 0 is null

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

Next Steps#

After migrating and updating to the Netcode package, we recommend looking into the following: