Polymorphism and interfaces

Question

So I have two set of game objects: Damage Dealers and Damage Takers.

The former implements this interface:

 public interface IDamageDealer
 {
     int Damage { get; set; }
 }

The latter implements this one:

 interface IDamagable 
 {
     void hitReg(IDamageDealer dd);
 }

In the OnCollisionEnter methods of the DamageDealers I want to deal damage to a Game Object if it is a Damage Taker without knowing exactly what type of Damage Taker it is.

So I added a specific tag to the Damage Takers and tried to get their script component which implements the interface IDamageDealer:

 void OnCollisionEnter(Collision collisionDetails) 
 {
     GameObject other = collisionDetails.gameObject;
     
     if(other.tag == Constants.DAMAGABLE_TAG)
     {
         other.GetComponent<IDamagable>().hitReg(this.damage);
     }
     ///...
 }

This does not work since in Unity the type parameter of this method call must be of type `UnityEngine.Component.

Is there a generic built in way to deal with this situation un Unity?

In the meantime I added an extension method to solve my problem. I hope it helps someone:

 public static class ExtensionMethods
 {
     public static T GetComponentByInterface<T>(this GameObject go) where T : class
     {
         T ret = null;
         foreach (var component in go.GetComponents<MonoBehaviour>())
         {
             T current = component as T;
             if(current != null)
             {
                 if (ret == null)
                     ret = current;
                 else
                     throw new Exception(); // TODO: OWN EXCEPTION
             }
         }

         return ret;
     }
 }

Answer 1

Best Answer

Answer by Bunny83 · Dec 09, 2014 at 12:50 AM

No, there isn't a generic way but you can use the non generic function. The generic GetComponent is actually just a wrapper for the System.Type version.

So instead of

 other.GetComponent<IDamagable>();

you can do

 (IDamagable)other.GetComponent(typeof(IDamagable));

As extension method it could look like this:

 public static T GetInterface<T>(this GameObject aGO) where T : class
 {
     return aGO.GetComponent(typeof(T)) as T;
 }
 public static T GetInterface<T>(this Component aComponent)  where T : class
 {
     return aComponent.GetComponent(typeof(T)) as T;
 }

I've posted them a couple of times here on UA ^^

Add comment · Show 3 · Share

Kiwasi · Dec 09, 2014 at 07:11 AM 0

Share

This is pretty good.

But since 4.6 came out, for the simple functionality described in the OP might be better served by using the event system.

VSZM · Dec 09, 2014 at 07:33 AM 0

Share

Is there a tutorial about the new event system?

Kiwasi · Dec 09, 2014 at 10:00 AM 1

Share

Not that I've found, it almost seems to have been overlooked in the release with the new UI tools. But in the long run its probably a more significant change. Goodbye Send$$anonymous$$essage.

Answer 2

Answer by Paulius-Liekis · Dec 09, 2014 at 12:55 AM

You could do:

  public abstract class IDamageDealer : MonoBehaviour
  {
      // your abstract stuff
  }

Of course this doesn't work when you need to implement/derive more than two interfaces.

Add comment · Show 1 · Share

VSZM · Dec 09, 2014 at 06:55 AM 0

Share

Yes, that is why I don't want to use this.

Polymorphism and interfaces

2 Replies

Your answer

Follow this Question

Related Questions