Question Finding Objects / Parameter use with Event Listeners

I've been starting to learn about using Events in my code, but have been running into a Problem using them where I seem to be missing a small difference between two cases:

First Method (Working fine)

Code (CSharp):

1.  
2. // Test Script
3.     UnityEvent TestEvent = new UnityEvent();
4.  
5.     private void Awake()
6.     {      
7.         TestEvent.AddListener(GameObject.Find("TestObject").GetComponent<UIObject>().Toggle);
8.     }

Just finding the Object in Scene, getting the Script-Component from it, and adding the (in this case) Toggle Method as the Listener for the Test Event works perfectly fine.


Second Method (Not working)

Code (CSharp):

1.  
2. // Test Script
3.     UnityEvent TestEvent = new UnityEvent();
4.  
5.     public void AddCustomListener(UIObject _object)
6.     {
7.         TestEvent.AddListener(_object.Toggle);
8.     }
9.  
10. // UIObject Script
11.     public void Start()
12.     {
13.         Test.Instance().AddCustomListener(this);
14.     }

I'd prefer to have the UIObjects to call the Manager Class (Test Class in this case) themselves instead of having the Manager look for everything themselves. So calling the AddCustomListener Method on the Test Script and having the UIObject be the Parameter, would be much easier (and flexible)
However when I use the UIObject in the AddCustomListener Method, actually adding the Listener on the TestEvent doesn't seem to work.

Can anyone explain to me the difference between those two cases?


EDIT: In case someone is wondering, I found the answer. Using "Instance()" to make the Test Class a Singleton messed things up. Getting a direct reference to the Script from the Scene makes it work. Just a mistake when mixing two approaches that made me confused.

 

What's "DefaultEvent"? It's not a builtin Unity class and you don't explain what it is here.

 

I'm sorry it's just an Override of a Unity Event, nothing really different about it. Changed in Post