Question Check if UnityEvent already contains a method without name check

Hi!,
I have a unity event that gets methods from different scripts. I want to make sure that the same method doesn't get added twice by accident.
The closest to I came to my solution is comparing the names of the methods. Which can cause issues if there are multiple scripts with the same method name.
What would be the best solution to my problem?

Here is a simplified test code:

Code (CSharp):

1.     [SerializeField] UnityEvent unityEvent;
2.  
3.     [ContextMenu("Test")]
4.     private void Test()
5.     {
6.         bool alreadyContains = false;
7.  
8.         for (int i = 0; i < unityEvent.GetPersistentEventCount(); i++)
9.         {
10.             //if (unityEvent.GetPersistentTarget(i) == MyMethod) //something like this
11.             if (unityEvent.GetPersistentMethodName(i) == nameof(MyMethod)) //this might cause issues with similar names
12.             {
13.                 Debug.Log("Already exists");
14.                 alreadyContains = true;
15.                 break;
16.             }
17.         }
18.  
19.         if (!alreadyContains)
20.         {
21.             UnityEventTools.AddPersistentListener(unityEvent, MyMethod);
22.         }
23.     }
24.  
25.     private void MyMethod() { }

 

I don´t know if it is a good solution, but you could use a Dictionary, with the script (-name) as key and the method name as value, so you could compare the script/key and the method/value.

 

Thanks. That gave me an idea to compare the target type.

Code (CSharp):

1.         for (int i = 0; i < unityEvent.GetPersistentEventCount(); i++)
2.         {
3.             if (unityEvent.GetPersistentTarget(i).GetType() == (typeof(TestScript))) //Added this
4.             {
5.                 if (unityEvent.GetPersistentMethodName(i) == nameof(MyMethod)) //this might cause issues
6.                 {
7.                     Debug.Log("Already exists");
8.                     alreadyContains = true;
9.                     break;
10.                 }
11.             }
12.         }

This should work in my case but still feels like a hack since there could be multiple instances of a script in the scene. Example: Multiple enemies with healthScript trying to addListener.

 

I think I figured it out. I think in this scenario, "object this" refers to the specific instance of the script. I can test against that to confirm. I haven't tested yet but this should be ok.

Code (CSharp):

1.         for (int i = 0; i < unityEvent.GetPersistentEventCount(); i++)
2.         {
3.             if (unityEvent.GetPersistentTarget(i) == this) //this          
4.             {
5.                 if (unityEvent.GetPersistentMethodName(i) == nameof(MyMethod))
6.                 {
7.                     Debug.Log("Already exists");
8.                     alreadyContains = true;
9.                     break;
10.                 }
11.             }
12.         }

I can't think of any scenario where this won't work. If anyone figures out a better way, please let me know.

 

Not sure if you can use this for your case, but I had a rare case where I wanted to prevent duplicated listeners and my lazy solution was to just call RemoveListener(MyMethod) directly before calling AddListener(MyMethod).

If the method was not added before the remove all will do nothing and it will be added, but if it was already there it will be removed and readded again, so it will never be added as a duplicate.

 

Actually, that fits my use case and sounds like should work fine. But, I already am using GetPersistentTarget(I). If that doesn't work out, I will try it. Thanks for the suggestion!