title: Android: Non-blocked screen on button click
body: <p>I've got a problem with a button click.
  When user clicks on my button, the screen is blocked for some seconds, because of the operations that activity has to execute.
  If I want to open a toast notification that displays a loading message, how I can execute theese operations in background?
  And if result is ok, how I can kill previous activity and open an other one?</p>