Fragment 与 旋转屏幕的细节处理

FragmentActivity中通过FragmentTransaction的add方法添加Fragment，当屏幕旋转时，会把Fragment添加两次，应该如此改写

if(savedInstanceState == null) {    mFragmentManager = getSupportFragmentManager();    FragmentTransaction fragmentTransaction = mFragmentManager.beginTransaction();    FragmentOne fragment = new FragmentOne();    fragmentTransaction.add(R.id.fragment_container, fragment);    fragmentTransaction.commit();}