Other script function call with variables

Question

Hello, I have class A with prefab populated from inspector. I'd like to call it from class B. I call it like below and got NullReference exception for Class's A prefabButton being null. How can I can the method from another class using destination class properties populated via inspector.

 public class A: MonoBehaviour {
     public GameObject prefabButton;
     public void FunctionA()
     {
       GameObject newButton = Instantiate(prefabButton) as GameObject;
     }
 }
 
 public class B: MonoBehaviour
 {
     public void FunctionB()
     {
         A populator = new A();
         populator.FunctionA(items);
     }
 }

Answer 1

Best Answer

Answer by sysameca · Feb 06, 2015 at 09:01 AM

It will be null, because you didn't assigned no game object to prefabButton. Your problem is that you are trying to create a MonoBehaviour with the new keyword instead of getting it as component. MonoBehaviour must be added to a game object and then the instance of the script is retreived through GetComponent().

Create a new object in the hierarchy name it ObjectA and add the A component to it.
Drag and drop your game object which you want to populate over the prefabButton inspector field.
Create a new game object in the hierarchy and add component B to it.
In class B's method FunctionB() instead of creating "new A()" replace it with: GameObject.Find("ObjectA").GetComponent().FunctionA();

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pesetskyps · Feb 06, 2015 at 09:07 AM 0

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Thanks, but this approach makes hard to apply software design patterns from "standard" program$$anonymous$$g that I knew before. :) Can you bring the light on this?

sysameca · Feb 06, 2015 at 09:17 AM 0

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Unity is entity-component based game engine. A lot of OOP practices can't be exactly achieved the same way you do in standard program$$anonymous$$g. It has it's pros i't has it's cons. I can explain for hours, but there are some other questions related to this so i will give you this link to start with. $$anonymous$$aybe the link is not 100% what you are looking for, but I am sure you can google the rest: How does unity entity system works

pesetskyps · Feb 06, 2015 at 09:19 AM 0

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The direction to read is exactly what I want, many thanks

sysameca · Feb 06, 2015 at 09:20 AM 0

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http://docs.unity3d.com/$$anonymous$$anual/UsingComponents.html

http://docs.unity3d.com/$$anonymous$$anual/TheGameObject-ComponentRelationship.html

Bonfire-Boy · Feb 06, 2015 at 09:32 AM 1

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@pesetskyps You can instantiate gameobjects in code, but you don't do it by calling a constructor. Classes derived from $$anonymous$$onobehaviour shouldn't have constructors, you don't create instances of them directly. Ins$$anonymous$$d you create a gameobject and attach components. The basic idiom is..

 GameObject go = new GameObject();
 go.AddComponent<A>();
 go.GetComponent<A>.initialisationFunction(...); // optional - if you need a function to set up the "A" component like a constructor would

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Other script function call with variables

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