Callback method to a destroyed object

Question

Hey all

I make a server call in which upon receiving a response, I call my callback method. The problem is that in rare situations, this callback method might be in a gameobject that has been destroyed. This is resulting

MissingReferenceException: The object of type 'xyz' has been destroyed but you are still trying to access it.

When I check if the callback is null, it is always returning false. Here is a sample code

   public class A : MonoBehaviour{
     
       private void initMethod(){
             B b_inst = new B();
             b.fetchResultsFromServer(myCallback);
      }
      private void myCallback(){
 
            Debug.Log("Success");
      }
 }
 
 public class B{
     Action callBack;
     public void fetchResultsFromServer(Action callBack){
            this.callBack =callBack;
            getResults();
      }
      private onResultReceived(){
           callBack();
     }
 
 }

So how can I handle this situation when orginalCaller who has the callback method is null. Is there a way I can pull the object from the callback to check if it is destroyed?

Thank you

Answer 1

Best Answer

Answer by JedBeryll · Aug 19, 2016 at 06:40 AM

Make the myCallBack method take a parameter.

 class A {
     private void initMethod(){
         B b_inst = new B();
 
         Action callbackAction = new Action(delegate {
             myCallback(this); //not sure if this is what you want to check but i guess you get the idea
         });
 
         b_inst.fetchResultsFromServer(callbackAction);
     }
 
     private void myCallback(A caller){
         if (caller == null) return;
 
         Debug.Log("Success");
     }
 }
 
 public class B{
     Action callBack;
 
     public void fetchResultsFromServer(Action callBack){
         this.callBack = callBack;
         getResults();
     }
 
     private void onResultReceived(){
         callBack();
     }
 
 }

Add comment · Show 1 · Share

arasem · Aug 22, 2016 at 12:35 AM 0

Share

Thank you. I was hoping I can check if it is null when I am at B. Because the moment you you call the callBack, you are in a null space (in which I can check if (this == null) and no need for parameter. So I wanted to know it is null when I am inside onResultReceived. I will accept it for now since no other answer and this is a valid one :)

Answer 2

Answer by jfonz001 · Sep 05, 2020 at 07:12 PM

Hey I'm 4 years late but if your object is destroyed but you still have a refrence to it somewhere it won't be seen as null if you do

if(destroyedObject == null)

instead do this

if(destroyedObject)

Add comment · Share

Callback method to a destroyed object

2 Replies

Your answer

Follow this Question

Related Questions