title: When to use setX and setY
body: <p>i am using setX and setY in order to move a view on the screen. However, i read that the android first needs to calculate the views positions, otherwise it gives NullPointerException (what happand to me).
  I need to know <strong>when</strong> to use it in order to avoid the exception. 
  Until now i used it in the onCreate().
  Thanks and have a good day</p>