[url]http://developer.android.com/guide/topics/ui/actionbar.html#ActionProvider[/url]
[url]http://stackoverflow.com/questions/19439106/cant-display-sub-menu-for-custom-actionprovider[/url]

Unfortunately, onPrepareSubMenu() is only called when onCreateActionView() returns null. Your solution (attaching a PopupMenu to the ImageView) will work, but since your ImageView is displaying an icon, you might consider just setting the icon in the menu XML and getting rid of the ImageView:

@Override
public View onCreateActionView(){
    return null;
}