Question by Fred_1996 · May 01, 2014 at 11:34 AM · 2d collision error collider trigger

Collision returning an error

Hi there, I have come across an problem that I can't solve.

This is part of my crate's script. When in collides, I want it to spawn a coin from the pool.

No errors show up in the console until the "rocket" (basically a bullet) collides with the box. I also have a rocket pool and all the rockets inside the hierarchy are clones of the original one. This is a 2D platformer/run'n'gun game.

  void OnCollisionEnter2D(Collision2D collision)
         {
             //Prepare coin spawn from pool and set to crate position
             GameObject obj = CoinPooling.current.GetPooledObject();
             if (obj == null) return;
             obj.transform.position = transform.position;
     
             if(collision.gameObject.tag == "Player") //If my player hits the crate spawn coin and set crate inactive 
             {
                 obj.SetActive(true);
     
                 gameObject.SetActive(false);
             }
             else if (collision.gameObject.tag == "Rocket")//Error seems to be here. 
                      //Spawn coin, deactivate crate, activate explosion particle system (attached to rocket), then deactivate rocket.

 
             {    
                 obj.SetActive(true);
                 
                 gameObject.SetActive(false);
     
                 collision.transform.FindChild("Explosion").gameObject.SetActive(true); //Trigger explosion
     
                 collision.gameObject.SetActive(false);
             }
     }

Do you have any idea why the error message is : Object Reference Not Set To An Instance Of An Object ?

Thank you in advance.

Add comment · Show 5

Yword · May 02, 2014 at 03:11 AM 0

Can you specify which line of code has error? I assume that "collision.transform.FindChild("Explosion")" is returning null, maybe the collided object does not has a child named "Explosion", or the child named "Explosion" is not active.

Fred_1996 · May 03, 2014 at 09:40 AM 0

Hi there, I double checked and all the game objects tagged "Rocket" have an Explosion game object as a child. However the Explosion game object is inactive. That is why I want to activate once before destroying adding the Rocket back into the pool. The line of code returning null is this one : else if (collision.gameObject.tag == "Rocket")

$$anonymous$$aybe I should create an "Explosion" pool and activate an explosion when needed ?

It is probably the way I coded this that is inefficient.

Pyrian · May 03, 2014 at 01:41 PM 0

I don't know why you're getting an error, but I can tell you that activating a child GameObject and then deactivating its parent results in an inactive child. If you inactivate a GameObject, all its children are effectively inactive, as well, regardless of their own active status.

Fred_1996 · May 03, 2014 at 07:49 PM 0

Hello, Pyrian thank you for your answer.

I actually solved the problem by creating an "explosion" pool and making explosions "independent". This improves performance, and it is easier to understand.

This is my new code :

 void OnCollisionEnter2D(Collision2D collision)
     {
         //Prepare coin spawn at crate position
         GameObject obj = CoinPooling.current.GetPooledObject();
         if (obj == null) return;
         obj.transform.position = transform.position;
 
 
         GameObject exp = ExplosionsPool.current$$anonymous$$GetPooledObject();
         if(exp == null) return;
 
 
 
         if(collision.gameObject.name == "Player")
         {
                         //Add 400 points to my overall score.
             Score$$anonymous$$eeper.score += 400;
         
 
             //Spawn coin
             obj.SetActive(true);
 
             //Deactivate crate
             gameObject.SetActive(false);
         }
         else if (collision.gameObject.tag == "Rocket")
         {    
             Score$$anonymous$$eeper.score += 400;
 
 
             //Spawn coin
             obj.SetActive(true);
 
             //Trigger explosion
             exp.transform.position = transform.position;
             exp.SetActive(true);
 
             //Set Rocket inactive
             collision.gameObject.SetActive(false);
 
             //Deactivate crate
             gameObject.SetActive(false);
         }
     }