title: When will the method "onPrepareOptionsMenu" be called?
body: <p>I create a menu.xml , only one action item with the "always" inside it.
  now I want to use the this method to change the menu's visible ,remove old action item , add new action item , change the old action item's icon ...
   so how to implement this ? 
  I don't want the onCreateOptionMenu to be called more than once as the activity has presented by Android system.</p>