title: Why use HandlerThread in Android
body: <p>In android , Handler can be used to post / handle message, if I don't use a HandlerThread (pass its Looper to Handler), does that mean in this case Handler use MainThread (UI Thread) 's Looper ? </p>
  
  <p>What result will get if Handler uses MainThread's Looper ? May cause mainThread blocked ?</p>