[UnityEvent] How can I add a Persistent Listener?

Question

The docs are unclear what the difference is between a persistent and non-persistent listener, and I have a bug around this code, could be my usage of the UnityEvent API. The 1st listener, Destroy enemy & respawn 1, is being called, but not the 2nd, call GMScore#AddScore.

UnityEvent#AddListener

Add a non persistent listener to the UnityEvent.

Use this to add a runtime callback.

UnityEvent#GetPersistentEventCount

Get the number of registered persistent listeners.

I feel like the missing info from the docs is just needs to answer: at what point does the listener become registered and persistent?

example usage:

define UnityEvent https://github.com/jtara1/Dooreo/blob/master/Assets/Scripts/Agents/Agent.cs#L12
add 1st Died listener https://github.com/jtara1/Dooreo/blob/master/Assets/Scripts/EnemyManager/EnemyManager.cs#L63
add 2nd Died listener https://github.com/jtara1/Dooreo/blob/master/Assets/Scripts/GameManager/GameManager.cs#L19
Invoke event emitter https://github.com/jtara1/Dooreo/blob/master/Assets/Scripts/Agents/Agent.cs#L30

Answer 1

Best Answer

Answer by Hellium · Oct 28, 2019 at 06:14 AM

A persistent listener is a listener which is specified at edit time (not in play mode) and will be serialised by Unity (saved persistently into the scene/prefab). This listener will be visible in the inspector. The AddPersistentListener is a function of the UnityEditor namespace, so it can't be called in a built game.

A "simple" listener is a listener bound at runtime that won't be saved into your scene/prefab, with a limited lifetime (destroyed if callback is removed or if holder gameObject is destroyed).

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unity_Nb1wks2d_zteKg · Oct 29, 2019 at 03:14 AM 0

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Thanks, that helped me understand and find my logic errors in usage of this. My problems

I was adding the listener to destroy the enemy before the listener to add score based on enemy score value
I was expecting GetPersistentEventCount() to return the count of callbacks, not just persistent ones.

implementation of UnityEventBase#Invoke

 protected void Invoke(object[] parameters)
 {
   List baseInvokableCallList = this.PrepareInvoke();
   for (int index = 0; index < baseInvokableCallList.Count; ++index)
     baseInvokableCallList[index].Invoke(parameters);
 }

[UnityEvent] How can I add a Persistent Listener?

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