Is there a Function Callback for when a vairable is altered in the Inspector?

I am writing a custom editor where GameObjects in the scene view are connected with lines using Handle.DrawLine. To "Connect" the GameObjects each contains a script w$$anonymous$$ch holds a List w$$anonymous$$ch can be filled using inspector by dragging other GameObjects from the $$anonymous$$erarchy.

Is there a function that the Editor can inherit or a delegate that detects when t$$anonymous$$s drop action into the List happens ie when a variable is changed from the inspector?

Thanks!