Selecting a GameObject to access attached metadata

Unity Engine
1

I’m having trouble wiring up the business logic to a prefab GameObject.

When instantiating the prefab, I attach the meta data as follows:

GameObject go = Instantiate (monsterPrefab, monsterPosition, Quaternion.identity);
MonsterObject monsterObj = go.AddComponent(typeof(MonsterObject )) as MonsterObject ;
// monsterObj is good
monsterObj.property = 1000;

Then when the user clicks on the monster in the game, I’d like to access the MonsterObject. In the monsterPrefab, I have an EventTrigger with a PointerClick event that calls a script and method “Selection.MonsterSelected” callback. A separate “Selection.cs” script is contained in an otherwise empty GameObject (“Selection”) that I dragged into the EventTrigger to access the Selection::MonsterSelected() callback from the drop down menu.

When MonsterSelected is called, I assume that code is running a component attached to my instantiated GameObject. From that callback, I try to access the MonsterObject component, but get a null pointer:

// monsterObj is null
MonsterObject monsterObj = GetComponent (typeof(MonsterObject)) as MonsterObject;

Does anyone know how I can attach script containing business logic and metadata to an instantiated prefab, and then access that object after clicking on it?

2

Spent more time on this one, but I’m still confused where my EventTrigger callback lives.

The InstanceID of my GameObject, go, above, is something like -11332, similar to other GameObjects and component ID’s. However from my Selection.cs script PointerClicked callback, GetComponent and GetComponentInParent are not finding the MonsterObject.

Does my EventTrigger just live in a Prefab, from which I cannot access any instantiated components? If so, how do I reference the instantiated GameObject and it’s components from an EventTrigger?

3

Just wanted to summarize my results on this in case anyone else runs into the same problem. I did’t represent the whole MonsterObject above, but basically, it was a base class that derived from MonoBehavior, and was subclassed by different monster types.

I ended up trashing that code and starting over before understanding where my problem was, but my new solution for attaching metadata to a GameObject works well. My new design is to represent each creature as two classes:

  1. A Unity class deriving from MonoObject that only contains methods to interact with the scene graph, such as selection and animation.
  2. A business logic parent class that does not derive from MonoObject, with derived classes for specific creature types to handle game state management (AI, combat, etc)

The unity class has a member variable that references the second business logic class, and comes pre-attached as a component to the prefab so that when I Instantiate() the prefab and get back a game object, the Unity class is already created. So after the Instantiate, I call “new” on the second business logic class and store the reference to it in the unity class, so the animation and selection routines can access game state if necessary.