Correct way to connect an instance of a class to a GameObject mesh

Question

I have a model with an animator; and a controller script to make it move, then I created a simple class called "TheEntity", which hold a name, and an int for the energy. When the time goes by, the energy goes down, so the mesh walk around or perform animations at random.

public class TheEntity()
{
    public string name;
    public int energy;

    public TheEntity()
    {
        // make a random name
        name = "joe"+ rnd.next(1,1000).toString();
        energy = rnd.next(20, 100);
    }

}

When the energy value goes to 0, the mesh "goes to sleep", and regenerate again in a certain amount of time.

If I have a list of TheEntity instances, as it would be if I have a list of NPC, what would be the correct way to assign a mesh to each entity class in the list?

Should I have a script on the mesh, that has a reference to a TheEntity class. and assign it at runtime when I load the mesh prefab? Or should I put the whole "TheEntity" class script on the mesh, and save it as prefab, so every time that I load the prefab, I will have a mesh with a related TheEntity instance directly?

Answer 1

1. "Things" in the Unity scene are GameObject , that's all there is to it.

2. Your class must be a MonoBehaviour to be on a game object.

3. In Unity, everything is a MonoBehaviour (a Component). There is, quite literally, nothing else whatsoever in Unity.

(Of course, you may have some "raw" non-Unity classes for things like say math calculations, but that's irrelevant.)

It's just that simple.

public Class Entity:Monobehaviour
{
}

attach that to an empty game object. Add the models (meshes) .. or whatever you want. Add sound effects, add anything.

Regarding "changing the mesh", no problem.

Do that in a routine in Entity, if you like.

public Class Entity:Monobehaviour
{
public void ChooseRandomMesh()
{
}
public void ChooseRandomColorPattern()
{
}
public void RunForTheHills()
{
}
public void AttackHero()
{
}
}

If you prefer, write a Component which does nothing other than randomly change the mesh.

public Class Entity:Monobehaviour
{
public void RandomizeEntity()
{
}
public void ChooseRandomColorPattern()
{
}
}

.. and attach that script to the game object, also.

In Unity, everything is a MonoBehaviour (a Component), it's that simple.

Regarding making it a prefab, if you want to, sure do that. Read any of thousands of tutorials on prefabs.

---

There's a critical comment you made in your comments below:

"Also the entity class is not MonoBehaviour..."

Here's an incredibly critical point in understanding Unity:

1) You're quite right that your "model" or "AI" or "database connection" sort of has "nothing to do" with unity game objects. (They of course don't have a "position" or "mass!" or anything, right?!)

HOWEVER HOWEVER HOWEVER HOWEVER HOWEVER HOWEVER HOWEVER HOWEVER HOWEVER

2) In Unity unless a class is a MonoBehaviour: you can't do anything with it/ You can't even access the run loop, it's a total nonstarter.

THUS THUS THUS THUS THUS THUS THUS THUS THUS THUS THUS THUS THUS THUS

3) In Unity all the stuff like that, IS IN FACT a MonoBehaviour AND YOU SIMPLY sit it on an empty game object. (Usually the name in the Heirarchy starts with underscore, say, so you know it's "not really" a conventional game object.)

The simple bottom line is in your preload scene (you must have one in 100% of projects) you have all your "AI" and "model" and "database" stuff, just sitting on one or more "pretend" markers (marker == otherwise empty game object).

Bottom line, when you say below "your model is not a MonoBehaviour" that is wrong. It will have to be a MonoBehaviour (if you think about it, it's absolutely inevitable you'll need to access the runloop, if nothing else) ... just make it a MonoBehaviour and put it on a marker, almost certainly in your preload.

I hope it makes sense. Essay on the topic.