[InjectOptional] attribute

[Metsker]

My typical workflow, while building multiplayer games is to gather data from the clients in a lobby, for example, selected characters/cosmetics, then, on the host, inject this data to the next scene.
So, in the next scene, this data is expected somewhere, to use right prefabs for spawning etc. Using Zenject, I could use [InjectOptional] to ignore these dependencies on the clients, but, using VContainer, to not get exceptions, my only workaround is to use IObjectResolver instead, which hides dependencies and requires much more boilerplate.
Maybe I am missing something, or you have suggestions for a better architecture

[tigran-sargsyan-w]

VContainer doesn’t have a Zenject-style [InjectOptional]. Optional constructor params aren’t supported, so you won’t get a “skip if missing” behavior on ctor injection. Use either (A) IObjectResolver.TryResolve(...) in a method/property injection, or (B) a Null-object / conditional registration per host vs client.

A) “Optional” via TryResolve

Register the data only on the host scope (optionally under a key), then probe for it in the next scene:

public sealed class HostScope : LifetimeScope
{
    protected override void Configure(IContainerBuilder b)
    {
        // e.g. after lobby collects selections
        b.RegisterInstance(lobbyData)
         .As<ILobbyData>()
         .WithParameter("Scene", "Next"); // or .Keyed(LobbyKey.Match)
    }
}

// Next scene — don't depend on ctor injection for this
public sealed class MatchBootstrap : MonoBehaviour
{
    [Inject]
    public void Construct(IObjectResolver container /*, other required deps */)
    {
        // if you keyed it: container.TryResolve<ILobbyData>(LobbyKey.Match, out var data)
        if (container.TryResolve<ILobbyData>(out var data))
        {
            spawner.Spawn(data.SelectedCharacterPrefab);
        }
        else
        {
            // client path: pick defaults or skip
        }
    }
}

Why this works: optional ctor deps aren’t supported in VContainer, but method/property injection + IObjectResolver.TryResolve(...) lets you branch without exceptions. Docs: constructor limitation and container API with TryResolve (incl. keyed).

B) Null-object / conditional registration

Another clean pattern is to always inject ILobbyData, but register a NullLobbyData on clients and a real one on host:

{
    public GameObject SelectedCharacterPrefab => default; // sensible defaults
}

#if CLIENT_BUILD
builder.Register<NullLobbyData, ILobbyData>(Lifetime.Singleton);
#else // HOST
builder.RegisterInstance(realLobbyData).As<ILobbyData>();
#endif

This keeps your constructors strict (no “optional”) and removes branching from call sites.

Notes / refs:

• Optional deps are not supported in constructors.
• Use method/property injection when you can’t (or shouldn’t) use ctors.
• IObjectResolver is the intended escape hatch; TryResolve (also with keys) is documented.

If this helps, please mark as Accepted — happy to tweak with your exact lobby flow.