title: Unity Listener/Event like OnValueChanged for GameObject properties
body: <p>I want to call a function each time my gameObject.renderer.isVisible is set to false without using <code>Update(){ 
      if(gameObject.renderer.isVisible == false)
          FunctionToCall(); 
  }</code>
  It's quite ugly.</p>
  
  <p>So I was wondering how can I make a Listener/Event like OnValueChanged(bool ) for GameObject properties and scripts variables in general ?
  Maybe there is an easier way, I'm new to Unity so maybe I'm missing something. </p>
  
  <p>Thanks and sorry for my poor english </p>