[Documentation] UnityEvent.RemoveAllListeners() only removes non persistent listeners

Minor nitpicking on the UnityEvent doc page: http://docs.unity3d.com/ScriptReference/Events.UnityEvent.html

It sais "Remove all listeners from the event", but should be "Remove all non persistent listeners from the event".

May be worth correcting. Best wishes!

 

What do you mean by "non persistent listeners" ?

 

UnityEvent contains a list of delegates that are called upon an event (e.g. OnClick() in the Button UI component). If you add new delegates via inspector they are "persistent" and can't be removed by script. On the other hand, if you call UnityEvent.AddListener(UnityAction) by script, it will add a "non persistent" delegate, that will not show up in the inspector.

All public functions of UnityEvent only allow to remove "non persistent" listeners/delegates that were added by script. Those who were added via inspector only can be removed via the inspector. UnityEvent.RemoveAllListeners() implies to be able to remove "persistent" listeners although this is not true (tested!).

 

Thanks Nanity!

The whole persistent vs non-persistent listeners thing doesn't appear to be documented, so that was a helpful explanation.

With that info, I poked through the UnityEngine source and come up with a solution for adding inspector (persistent) events via script. You just have to use reflection to get at the private method AddPersistentListener, which expects a delegate reference (and optional CallState).

This is a problem I've found with the event system in general - not only is the documentation less than stellar, but it doesn't appear to have been set up with the intention of being heavily modifiable by the user. It's actually a rather nice system, and I hope they continue to expand it when they (someday) update the Input class, but hopefully in the meantime the community can continue to put together its own documentation and

 

It's a nice piece of code yes. If they would rip out Unity Editor Drawers as seperate dll, they would have to rewrite a bunch of code because they call a lot of internal functions that are not available to us.

Reflection works, but if you want to make deep changes you have so much clutter.

Improvements might to be taken up into the Documentation, not sure what's the best communication channel though. This forum? Bug reports? Mail to the support? PM to Unity Employees?

 

Thank you! I've been confused for a couple days why isn't adding/removing listeners working, been through countless google searches, until I found your post which explains what a persistent listener is, and that you can't manipulate one, and that non persistent listeners don't show up in inspector. Once I removed the persistent listeners, and added them through code, everything started working.

Wish I knew how to add/remove persistent listeners though.

 

Is there a method to count the number of non-persistent listeners?
Nothing in the documentation that I can see- there's GetPersistentEventCount, but as the name suggests, it only returns the number of persistent listeners.

 

It is worth noting that you can also remove persistent listeners from onClick event or any other event as following:

1. gameObject.GetComponent<Button>().onClick = new Button.ButtonClickedEvent();

 

Any update on if we will be able to get info on the non persistent listeners? Seems we can still only see the persistent ones. I would like to know how many non persistent listener are on an event.

 

If somebody need example how to remove persistent listener from code in editor, I found solution

Code (CSharp):

1.  
2.         //Button on which you want to remove persistent listeners
3.         Button inAppBackButton = inAppMenuGameObject.transform.GetChild(1).GetComponent<Button>();
4.  
5.         //Define what Method you want to call, and add it later as persistent listener
6.         UnityEngine.Events.UnityAction action = gameControllerMenu.menus.settings.GetComponent<SettingsMenu>().ClickSoundPlay;
7.         //or
8.         UnityEngine.Events.UnityAction action1 = new UnityEngine.Events.UnityAction(gameControllerMenu.menus.settings.GetComponent<SettingsMenu>().ClickSoundPlay);
9.  
10.         //Define method with one argument
11.         UnityEngine.Events.UnityAction<GameObject> actionWithGO = gameControllerMenu.menuManagerScript.ShowMenu;
12.         //or
13.         UnityEngine.Events.UnityAction<GameObject> actionWithGO1 = new UnityEngine.Events.UnityAction<GameObject>(gameControllerMenu.menuManagerScript.ShowMenu);
14.  
15.         //Remove all previous persistent listeners
16.         UnityEditor.Events.UnityEventTools.RemovePersistentListener(inAppBackButton.onClick, 1);
17.         UnityEditor.Events.UnityEventTools.RemovePersistentListener(inAppBackButton.onClick, 0);
18.  
19.         //Add new void persisten listener
20.         UnityEditor.Events.UnityEventTools.AddVoidPersistentListener(inAppBackButton.onClick, action);
21.  
22.         //Add new persistent listener with GameObject as argument
23.         UnityEditor.Events.UnityEventTools.AddObjectPersistentListener<GameObject>(inAppBackButton.onClick, actionWithGO, gameControllerMenu.menus.videoForCoinsMenu);
24.  

Hope someone will find it useful. Cheers.

 

But it's works only on editor, sad... :' (
Is there any way to make it works on runtime(build version)?

 

I would also be interested in hearing about workarounds for doing this in runtime. Thanks for the useful explanation @Nanity

 

https://docs.unity3d.com/ScriptReference/Events.UnityEventBase.RemoveAllListeners.html

@Nanity just to notify there is a typo on this page ... lol


Description

Remove all non-persisent (ie created from script) listeners from the event.
All persistent (ie created via inspector) listeners are not affected.

 

Hopefully, I found the solution for this problem, the solution is that we can change the UnityEventCallState to off. Let me show you an example:

I add these methods through the inspector,


Now, I want to disable their execution using script, So I wrote these lines of code to change Unity Event Call State.


Now in play mode,


Conclusion: If we cannot remove the persistent listeners from the script then we can turn off the Unity event call state using the script. So in this way, we can get rid of persistent listeners during gameplay. I hope my solution satisfies your need.