Send additional parameters to callback

Try the following:

Code (CSharp):

1. static void OnMouseUp(MouseUpEvent evt, Whatever we)
2. {
3.     // Do stuff.
4. }
5.  
6. void RegisterToElement(VisualElement ve, Whatever we)
7. {
8.     ve.RegisterCallback<MouseUpEvent, Whatever>(OnMouseUp, we);
9. }

 

All events have a target parameter that contains the element where the event originated from:

Code (CSharp):

1. void OnMouseUp(MouseUpEvent evt) {
2.     var button = evt.target as Button;
3.     ...
4. }

and Button specifically has an overload for its callback that takes an event as an argument:

Code (CSharp):

1. var button = new Button();
2. button.clickable.clickedWithEventInfo += (evt) => Debug.Log((evt.target as Button).name);