Setting any NetworkVariable after upgrading from 1.0.2 to 1.1.0 throws a NullReferenceException

[starchitectus]

After upgrading my project, network variables have completely broken.

I have tested in the project with this simple test script:

public class NetworkVariableTester : MonoBehaviour
{
    NetworkVariable<float> floatVariable = new();

    private void Update()
    {
        floatVariable.Value = Time.time;
    }
}

This throws the following error on every frame:

NullReferenceException: Object reference not set to an instance of an object
Unity.Netcode.NetworkVariable`1[T].set_Value (T value) (at Library/PackageCache/com.unity.netcode.gameobjects@1.1.0/Runtime/NetworkVariable/NetworkVariable.cs:53)
NetworkVariableTester.Update () (at Assets/NetworkVariableTester.cs:12)

This error seems to come from the NetworkVariableSerialization system that was added in 1.1.0. I'm not sure why it is broken in my project and no other users seem to be reporting errors. Any help would be appreciated as the project is completely unusable until this is fixed.

[jeffreyrainy]

I might be mistaken, but as far as I know (or as I've seen), NetworkVariable should only be in NetworkBehaviour, not MonoBehaviour. I'm surprised it would work.

If you change it from MonoBehaviour to NetworkBehaviour and if you allocate (new) the NetworkVariable in the Awake() member function of the NetworkBehaviour, everything should work.

[starchitectus]

Sorry, helps if my testing scripts are written correctly! I didn't notice when putting together the test script as it was throwing the same error as all my other scripts. (side note - this is a separate problem, I should have got a warning that my class was not a NetworkBehaviour!)

Testing now is producing some strange behaviour.
The following runs with no issues:

public class NetworkVariableTester : NetworkBehaviour
{
    NetworkVariable<float> floatVariable = new();

    private void Update()
    {
        floatVariable.Value = Time.time;
    }
}

However, when I try and use my custom NetworkVariable things will break. The SBPNetworkVariable is a simple wrapper that was working fine before the update:

public class NetworkVariableTester : NetworkBehaviour
{
    SBPNetworkVariable<float> floatVariable = new();

    private void Update()
    {
        floatVariable.Value = Time.time;
    }
}

public class SBPNetworkVariable<T> : NetworkVariable<T> where T : unmanaged
{
    public SBPNetworkVariable(
        T value = default, 
        NetworkVariableReadPermission readPerm = NetworkVariableReadPermission.Everyone, 
        NetworkVariableWritePermission writePerm = NetworkVariableWritePermission.Server) : base(value, readPerm, writePerm)
    {
    }

    public void Set(T newValue) => Value = newValue;
    public static implicit operator T(SBPNetworkVariable<T> v) => v.Value;
}

This produces the same error as before:

NullReferenceException: Object reference not set to an instance of an object
Unity.Netcode.NetworkVariable`1[T].set_Value (T value) (at Library/PackageCache/com.unity.netcode.gameobjects@1.2.0/Runtime/NetworkVariable/NetworkVariable.cs:53)
NetworkVariableTester.Update () (at Assets/NetworkVariableTester.cs:12)

The strangest thing is that the following script works just fine:

public class NetworkVariableTester : NetworkBehaviour
{
    NetworkVariable<float> floatVariable = new();
    SBPNetworkVariable<float> customFloatVariable = new();

    private void Update()
    {
        floatVariable.Value = Time.time;
        customFloatVariable.Value = Time.time;
    }
}

Whereas this one doesn't:

public class NetworkVariableTester : NetworkBehaviour
{
    NetworkVariable<int> floatVariable = new();
    SBPNetworkVariable<float> customFloatVariable = new();

    private void Update()
    {
        floatVariable.Value = (int)Time.time;
        customFloatVariable.Value = Time.time;
    }
}

Conclusion:

Custom NetworkVariables that inherit from NetworkVariable<T> are not initialized properly unless a NetworkVariable<T> is also present within the same script.

[jeffreyrainy]

public class NetworkVariableTester : NetworkBehaviour
 {
   SBPNetworkVariable<float> floatVariable = new();

Can you check if it works any better when you allocate the (SBP)NetworkVariable<float> in the Awake() function of the behaviour as opposed to directly in the declaration?

[starchitectus]

public class NetworkVariableTester : NetworkBehaviour
 {
   SBPNetworkVariable<float> floatVariable = new();

Can you check if it works any better when you allocate the (SBP)NetworkVariable<float> in the Awake() function of the behaviour as opposed to directly in the declaration?

Declaring in Awake has no impact.

Interestingly through, I have discovered the following setup will avoid the issue:

public class NetworkVariableTester : NetworkBehaviour
{
    NetworkVariable<float> floatVariable;

    private void Awake()
    {
        floatVariable = new();
    }

    private void Update()
    {
        floatVariable.Value = Time.time;
    }
}

public class CustomNetworkVariableTester : NetworkBehaviour
{
    SBPNetworkVariable<float> customFloatVariable;

    private void Awake()
    {
        customFloatVariable = new();
    }

    private void Update()
    {
        customFloatVariable.Value = Time.time;
    }
}

The CustomNetworkVariableTester will work even if the NetworkVariableTester is not present on any GameObjects.
This means the issue is limited to any custom NetworkVariable where T is not declared in a network variable anywhere else in the project.
So my workaround for now will be to maintain an unused script that declares an instance of NetworkVariable for every type of argument I'm passing over the network.

[ShadauxCat]

Just some history here: The reason we added the NetworkVariableSerialization stuff in 1.1.0 was to enable NetworkVariables to support managed types, as well as better support for generic types. In order to do that, we had to lean heavily on codegen in order to allow NetworkVariable to know how to serialize each type. Doing that meant that we had to find a way to compile a list of types that we need to generate serialization for.

The way that we currently compile the list is by looking through all NetworkBehaviour types, iterating the fields within the type, and looking for any field of type NetworkVariable<T> and then generating serialization code for that T. That's why adding NetworkVariable<float> to your test case made it start working - it allowed us to discover that you need us to be able to serialize floats and generate serialization code for that.

I'll update that code in the next release so it looks for anything that is or inherits from NetworkVariable<T>, which will fix your issue. In the mean time, the upshot of that knowledge is: You can address this by creating a dummy NetworkBehaviour somewhere in your code that has NetworkVariable<T> fields for every T you need to support, and that'll trigger the codegen to find it correctly. That NetworkBehaviour never has to be used anywhere, so you can just put it off in a file by itself and ignore it - that way it won't use up extra memory or bandwidth like putting it in the same class
as your custom NetworkVariable type would.

[starchitectus]

The way that we currently compile the list is by looking through all NetworkBehaviour types, iterating the fields within the type, and looking for any field of type NetworkVariable<T> and then generating serialization code for that T. That's why adding NetworkVariable<float> to your test case made it start working - it allowed us to discover that you need us to be able to serialize floats and generate serialization code for that.

I figured this must be the case, thanks for clarifying.

I'll update that code in the next release so it looks for anything that is or inherits from NetworkVariable<T>, which will fix your issue. In the mean time, the upshot of that knowledge is: You can address this by creating a dummy NetworkBehaviour somewhere in your code that has NetworkVariable<T> fields for every T you need to support, and that'll trigger the codegen to find it correctly. That NetworkBehaviour never has to be used anywhere, so you can just put it off in a file by itself and ignore it - that way it won't use up extra memory or bandwidth like putting it in the same class as your custom NetworkVariable type would.

I've got this set up now and can confirm that it works. Thanks for the quick response!