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I'm building a Raycast setup where game objects run code on click / touch.

if (Physics.Raycast(transform.position, transform.forward, out RaycastHit hit, maxDistance, interactableLayers))
     {
        
         if  (Input.GetButtonDown("Fire1"))
         {
             if (hit.collider != null) 
             { 

             currentInteractable = hit.collider.GetComponent<Interactable>();

             Debug.Log(hit.collider.name);

             }
         }

I'm following a tutorial where I must use an Interface to configure OnClick Actions for each game object:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 // public class Interactable : MonoBehaviour 
 
 // {
 
   public interface Interactable 
   {
 
     void onClickAction(); 
 
   }

However, I'm receiving a bunch of errors! I can't add this Interactable script to my game object and receive the error: "Can't add script behaviour Interactable. The script class can't be abstract!"

I also see in the console: "'Interactable' is missing the class attribute 'ExtensionOfNativeClass'!"

Why is this happening?

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    \$\begingroup\$ I think you may have mistyped something from the tutorial. (Or the tutorial has mistyped something.) Specifically, look at the words after public - class vs interface. \$\endgroup\$ Commented Apr 18, 2022 at 17:48
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    \$\begingroup\$ "I'm following a tutorial" - conventionally, this is where you would include a link to said tutorial, so users here can help identify whether the tutorial itself is wrong, or whether you've made an error in following it. Did the tutorial perhaps include a step where you create a MonoBehaviour-derived class that implements the Interactable interface? \$\endgroup\$ Commented Apr 18, 2022 at 21:38
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    \$\begingroup\$ Do you understand what interfaces in the C# programming language actually are and what they do? When the tutorial you are using expects you to know that and you don't, then you might want to learn that first. \$\endgroup\$ Commented Apr 19, 2022 at 11:38

1 Answer 1

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An interface is not a script.

An interface describes what public methods certain scripts (or more accurately, classes) are supposed to have. This code here:

public interface Interactable 
{ 
    void OnClickAction();  
}

says, is that any script which is an "Interactible" should have a method void OnClickAction(). How it implements that method is up to the script, but when it wants to be an "Interactible", it needs that method.

OK, but how do you say that a certain script is supposed to be an interactible? Like this:

public class SomeScript: MonoBehaviour, Interactible
{

What this code says is "This class here is a Unity MonoBehaviour (so it can be added as a component to a GameObject), and it is also an Interactible". When you write this, you will notice that there is an error stating that SomeScript says that it implements the "Interactible" interface, but does not have the method void OnClickAction() like an "Interactible" is supposed to. So you need to implement it.

public class SomeScript: MonoBehaviour, Interactible
{
     public void OnClickAction() {
         Debug.Log($"OnClickAction called on { name }");
     }
}

OK, but what's the purpose of all this? Because it allows you to write code like this:

Interactible currentInteractable = hit.collider.GetComponent<Interactable>();
currentInteractible.OnClickAction();

The method GetComponent<Interactable>() returns the first script on an object which implements Interactible, regardless of what type it is. Note that the return value of this method is of type Interactible. Which means that you can only call methods on it which are part of the interactible interface. Which in this case is only one method: OnClickAction(). What this allows you to do is to have many scripts on different kinds of gameObjects which all do different things, but all implement the interface Interactible with an OnClickAction() method. So you can call that method on those scripts regardless of what class they actually have.

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