Only run a system when all of its [Inject] are satisfied?

Currently the system does not run when there are no entity match in all [Inject]s. But if even one struct group was injected the system will run with other unmatched injects having length 0.

My current problem is I have some entities holding very important data (game states, deltaTime for everyone, etc.) that is going to be almost always available. And now there are some system which I want them to only run when a certain component tags are attached to my other entities.

That entity runs all the time since I have 2 [Injects] and one of them is always available. What I do is I always have to explicitly check the length of the second one should it really continue the system or not but I would prefer if the system automatically AND 2 injects together in the first place. How do you approach this problem?

I tried removing the always occurring [Inject] out, and use GetComponentGroup inside the OnUpdate logic instead. It works only before the first OnUpdate trigger, then from that point it *seems* like GetComponentGroup somehow adds to the system's Inject permanently and does not stop running ever again? (Like I have 2 [Inject] in the first place, only delayed. Things works according to my wish until after the first OnUpdate)

(I think about `ISharedComponentData` before, but it seems to be for sharing the same data for many entity and for a "rarely changed" data as the doc says, but this data changes in every frame.)

 

I'm curious as to what is a good design pattern for storing global data as well. Whether we should store it in Components and inject into every system or whether it's better to store it in static classes or injected systems.

Injecting the same group into every system feels a bit like multiple inheritance. It effectively keeps all systems on all the time.
But then maybe storing settings in components is the best way for working with the job system mechanics?

In any event, I agree that it might be useful to have ability to require all groups before running a system. I have systems which process a parent group and a related child group. In some cases if there's no parents, there's no point iterating the children so it would be useful to be able to specify that criteria on injection groups.

 

By the way what's working right now for me is to access the global data not via Inject, but by remembering its Entity ID on a static variable then I could use `EntityManager` built in variable in `ComponentSystem` to access it while in `OnUpdate`, (run when system already triggered) without adding to the system activation requirement.

And in the latest 0.0.6 build I could use `ArchetypeChunkArray` to get the data without static variables from outside without affecting system activation, making the system more modular.

I blogged both ways in more details here : https://medium.com/gametorrahod/unity-ecs-the-system-is-always-running-ed3cdd60f885

Anyways seems like touching anything related to `ComponentGroup` magically makes the system "Inject" the group forever. Both static entity ID and ACA avoids that BUT with that I believe the automatic dependency management would not work anymore against the type I "cheated". Really needs an inject-based way to do this?

 

I haven't really looked into this myself, but I suspect putting this global state in a SharedComponent should suffice. This way you won't be requiring two different arrays to be injected, but rather only one, which if there aren't any entities it will be ignored.